The Body Temperature Software (BTS) App is a software-only mobile medical application intended for over-the- counter (OTC) use with compatible mobile computing platforms that includes a general purpose infrared sensor for the intermittent determination of human body temperature on people of all ages.

Device Description

The Body Temperature Software ("BTS") mobile application ("App"), is a Software as a Medical Device (SaMD) that leverages an infrared sensor from qualified compatible general computing platforms (i.e. Google Pixel Smartphone) to provide on-demand body temperature measurements. The BTS App is based on well understood infrared measurement technology. The app leverages consumer general purpose computing platforms to collect the inputs for measurement.

The BTS App is intended to be operated by users above 18 years of age and can be used to measure body temperature for themselves or other individuals. To collect the input temperature data, the user is guided to conduct a non-contact forehead sweep starting at the center of the forehead and ending at the temple, thereby passing over the temporal artery, which corresponds to the highest temperature point on the forehead. This temperature data is then used as an input into the BTS App to convert the measured skin temperature data into a body temperature value. Before and during this measurement process, the BTS App performs a series of signal quality checks to ensure the validity of the temperature data collected. Additionally, to aid users with the interpretation of their measurements, the BTS App also has the option to present users with a color-coded temperature quide to indicate if the measurement falls within normal limits or indicative of an elevated state based on wellrecognized body temperature ranges for the specified age of the individual being measured.

The BTS App collects the temporal artery temperature, which is processed using a polynomial function to approximate a rectal temperature.

AI/ML Overview

Here's a breakdown of the acceptance criteria and study information for the Body Temperature Software (BTS) based on the provided document:

1. Table of Acceptance Criteria and Reported Device Performance

Acceptance Criteria	Reported Device Performance
Laboratory Accuracy	±0.5°F (±0.3°C)
Measurement Range	94.1°F-109.4°F (34.5°C-43°C)

2. Sample Size Used for the Test Set and Data Provenance

The document does not explicitly state the sample size used for the test set or the data provenance (e.g., country of origin, retrospective or prospective). It mentions "Validation Testing" and "Laboratory accuracy testing," implying a test set was used, but details are omitted in this summary.

3. Number of Experts and Qualifications for Ground Truth Establishment

Not applicable. The document describes laboratory accuracy testing based on a "reference body rectal site" and adherence to ISO standards, not expert-established ground truth.

4. Adjudication Method for the Test Set

Not applicable. The reported testing focuses on device accuracy against a physical reference (rectal temperature) in a laboratory setting, not subjective expert judgment requiring adjudication.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No, a multi-reader multi-case (MRMC) comparative effectiveness study was not done. The document focuses on the device's standalone performance and its equivalence to a predicate device, not on human reader improvement with or without AI assistance.

6. Standalone (Algorithm Only Without Human-in-the-Loop Performance) Study

Yes, a standalone (algorithm only) performance study was conducted. The "Laboratory Accuracy" data, demonstrating ±0.3°C accuracy, directly reflects the algorithm's performance in determining body temperature from IR sensor input. The device description explicitly states it's a "Software as a Medical Device (SaMD)" that processes sensor data.

7. Type of Ground Truth Used

The ground truth used for the accuracy assessment was a reference body rectal site. The BTS app "processes the sensor data collected during the sweep and determines the body temperature" and "The displayed temperature is that of the temporal artery which is processed using a polynomial function to approximate a rectal temperature."

8. Sample Size for the Training Set

The document does not specify the sample size for the training set. It mentions the "BTS App is based on well understood infrared measurement technology" and "The BTS App collects the temporal artery temperature, which is processed using a polynomial function to approximate a rectal temperature," suggesting the algorithm was developed and trained prior to this specific premarket notification, but details regarding its training are not provided in this summary.

9. How the Ground Truth for the Training Set Was Established

The document does not detail how the ground truth for the training set was established. It primarily focuses on the device's performance validation against a predicate and ISO standards. Given the use of a "polynomial function to approximate a rectal temperature," it's highly likely that the model was trained using paired temporal artery temperature readings and corresponding rectal temperature measurements as ground truth, but the specifics of this process are not included in this submission summary.

Summary

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February 13, 2025

Fitbit LLC Nathan Austin Lead Regulatory Affairs Technical Program Manager 215 Fremont St San Francisco, California 94105

Re: K243778

Trade/Device Name: Body Temperature Software (BTS) Regulation Number: 21 CFR 880.2915 Regulation Name: Body Temperature Sensing Software Regulatory Class: Class II Product Code: QZA Dated: December 4, 2024 Received: December 9, 2024

Dear Nathan Austin:

We have reviewed your section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (the Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. Although this letter refers to your product as a device, please be aware that some cleared products may instead be combination products. The 510(k) Premarket Notification Database available at https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm identifies combination product submissions. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.

If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

Additional information about changes that may require a new premarket notification are provided in the FDA guidance documents entitled "Deciding When to Submit a 510(k) for a Change to an Existing Device"

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(https://www.fda.gov/media/99812/download) and "Deciding When to Submit a 510(k) for a Software Change to an Existing Device" (https://www.fda.gov/media/99785/download).

Your device is also subject to, among other requirements, the Quality System (QS) regulation (21 CFR Part 820), which includes, but is not limited to, 21 CFR 820.30. Design controls; 21 CFR 820.90. Nonconforming product; and 21 CFR 820.100, Corrective and preventive action. Please note that regardless of whether a change requires premarket review. the OS regulation requires device manufacturers to review and approve changes to device design and production (21 CFR 820.30 and 21 CFR 820.70) and document changes and approvals in the device master record (21 CFR 820.181).

Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part 801); medical device reporting of medical device-related adverse events) (21 CFR Part 803) for devices or postmarketing safety reporting (21 CFR Part 4, Subpart B) for combination products (see https://www.fda.gov/combination-products/guidance-regulatory-information/postmarketing-safety-reportingcombination-products); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820) for devices or current good manufacturing practices (21 CFR Part 4, Subpart A) for combination products; and, if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR Parts 1000-1050.

All medical devices, including Class I and unclassified devices and combination product device constituent parts are required to be in compliance with the final Unique Device Identification System rule ("UDI Rue"). The UDI Rule requires, among other things, that a device bear a unique device identifier (UDI) on its label and package (21 CFR 801.20(a)) unless an exception or alternative applies (21 CFR 801.20(b)) and that the dates on the device label be formatted in accordance with 21 CFR 801.18. The UDI Rule (21 CFR 830.300(a) and 830.320(b)) also requires that certain information be submitted to the Global Unique Device Identification Database (GUDID) (21 CFR Part 830 Subpart E). For additional information on these requirements, please see the UDI System webpage at https://www.fda.gov/medical-devices/device-advicecomprehensive-regulatory-assistance/unique-device-identification-system-udi-system.

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to https://www.fda.gov/medical-device-safety/medical-device-reportingmdr-how-report-medical-device-problems.

For comprehensive regulatory information about mediation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/medicaldevices/device-advice-comprehensive-regulatory-assistance) and CDRH Learn (https://www.fda.gov/training-and-continuing-education/cdrh-learn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (https://www.fda.gov/medical-device-advice-comprehensive-regulatoryassistance/contact-us-division-industry-and-consumer-education-dice) for more information or contact DICE by email (DICE@fda.hhs.gov) or phone (1-800-638-2041 or 301-796-7100).

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Sincerely,

Porsche Bennett

Porsche Bennett For David Wolloscheck Ph.D. Assistant Director DHT3C: Division of Drug Delivery and General Hospital Devices, and Human Factors OHT3: Office of Gastrorenal, ObGyn, General Hospital, and Urology Devices Office of Product Evaluation and Quality Center for Devices and Radiological Health

Enclosure

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Indications for Use

510(k) Number (if known) K243778

Device Name Body Temperature Software (BTS)

Indications for Use (Describe)

Type of Use (Select one or both, as applicable)
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Prescription Use (Part 21 CFR 801 Subpart D)

|X | Over-The-Counter Use (21 CFR 801 Subpart C)

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K243778- 510k Summary

This Premarket Notification is submitted by:

Fitbit, LLC. 215 Fremont Street, San Francisco, CA 94105

Contact Information:

Contact Person: Nathan Austin Phone: (650) 447-9336 Email: nathanaustin@google.com Date Prepared: February 13, 2025

Device Trade Name: Body Temperature Software (BTS)

Subject Device Information
Device Classification Name	Body temperature sensing software
Review Panel	General Hospital
Product Code & Regulation Number	QZA - 21 CFR 880.2915
Regulatory Class	Class II
510k Number	K243778

Predicate Device:

The legally marketed predicate for the subject device is detailed in the table below.

Predicate DeviceTrade Name	De Novo	Product Code	Manufacturer
Body TemperatureSoftware (BTS)	DEN230050	QZA	Fitbit LLC

Indications for Use:

The Body Temperature Software (BTS) App is a software-only mobile medical application intended for over-the-counter (OTC) use with compatible mobile computing platforms that includes a general purpose infrared sensor for the intermittent determination of human body temperature on people of all ages.

Device Description:

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The BTS App collects the temporal artery temperature, which is processed using a polynomial function to approximate a rectal temperature. The following are the key performance specifications for the BTS App:

Human Body Temperature Measurement Range: 94.1°F-109.4°F (34.5°C-43°C) ●
o Laboratory Accuracy (Max): ±0.5°F (±0.3°C)

Operating Ambient Temperature:

Temperature: 59.0°F-95°F (15°C-35°C)
Humidity: Humidity Per ASTM E1965-98, up to 95% non-condensing ●
Display Resolution: 0.1℃ / 0.1°F ●
Temperature Scales: Degrees °C / °F ●
Storage Conditions (temperature/humidity): -20°C 40°C (-4°F 113°F); Humidity ● up to 95% non-condensing
Display Modes: Displayed temperature is the temperature of the temporal artery plus a mathematical adjustment to approximate rectal temperature.

The changes subject to this special 510k are the pre-measurement checks and values that are replaced by binary flags to ensure a body temperature measurement is only enabled when the appropriate conditions are met. These flags are:

1. Sensor too warm flag
1. Sensor too cold flag
1. Difference too high flaq
1. Skin too warm flag
1. Skin too cold flag

Additionally, the range for the sensor too warm/too cold flag is hardware dependent and no longer a set value.

Comparison of Technological Characteristics:

A summary of substantial equivalence between the subject device and predicate device included in the scope of this Special 510(k) is included in the table below.

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Table 1: Summary of Substantial Equivalence

	Subject DeviceBody Temperature Software	Predicate DeviceBody Temperature Software(DEN230050)	Equivalence Discussion
Indications foruse	The Body Temperature Software(BTS) App is a software-only mobilemedical application intended for over-the-counter (OTC) use withcompatible mobile computingplatforms that includes a generalpurpose infrared sensor for theintermittent determination of humanbody temperature on people of allages.	The Body Temperature Software(BTS) App is a software-only mobilemedical application intended for over-the-counter (OTC) use with compatiblemobile computing platforms thatincludes a general purpose infraredsensor for the intermittentdetermination of human bodytemperature on people of all ages.	Same
Intended User	The BTS App is intended to beoperated by users above 18 years ofage.	The BTS App is intended to beoperated by users above 18 years ofage.	Same
DeviceClassification	Class II	Class II	Same
FDA ProductCode andRegulatoryClassification	QZA - 21 CFR 880.2915Body temperature sensing software	QZA - 21 CFR 880.2915Body temperature sensing software	Same
PatientPopulation	General population excludingpremature/preterm infants	General population excludingpremature/preterm infants	Same
Prescription	OTC	OTC	Same
or OTC
AnatomicalSite	Forehead using a compatibleconsumer smartphone with IRsensors.	Forehead using a compatibleconsumer smartphone with IR sensors.	Same
UseEnvironment	Home/General Use	Home/General Use	Same
Compatibledevices	Pixel 8 Pro and other consumer Pixelsmartphone devices deemedcompatible with Android 14 operatingsystem release or higher	Pixel 8 Pro with Android 14 operatingsystem release or higher	DifferentThe BTS App is deemedcompatible with additionalhardware platforms that meet thepre-specified requirements. Thisaddition is to include additionalconsumer Pixel smartphonesas compatible devices anddoes not raise new questions ofsafety and effectiveness.
Inputs to BTS	1. Range flag and IR sensor check2. A temperature signal that qualifiedsmartphone devices generate.a. The Sensor AmbientTemperature is set toHardware specificranges.b. Skin too warm/coldchecks are binaryflags.c. Window temperaturedifference too highcheck is a binary flag.	1. Range flag and IR sensor check2. A temperature signal that qualifiedsmartphone devices generate.a. The Sensor AmbientTemperature parameteris set at 15°C to 35°C	DifferentThe subject device uses binaryflags to check for suitable pre-measurement phone hardwareconditions. These functions occuroutside the SaMD and aremaintained in a hardwarespecification table.The Sensor AmbientTemperature is set to Hardware
			specific ranges with the subjectdevice instead of a defined range.Validated laboratory accuracytesting for the sensor ambienttemperature range supports thechange not raising new questionsof safety and effectiveness.The skin too warm/cold andthe difference too high flagshave been modified to bebinary flags instead ofspecified ranges. Thisdifference is evaluated usingsoftware verification and doesnot raise new questions ofsafety and effectiveness.
Principle ofoperation	A user's temperature is measuredwhen a forehead measurementsweep is performed with the infraredsensor and the signal input data isprovided by the platform to the BTSApp algorithm.The BTS App performs a series ofchecks prior to launching, during thesweep and during the processing ofthe signal to ensure that thetemperature data collected is valid forprocessing. Using this valid collected	A user's temperature is measuredwhen a forehead measurement sweepis performed with the infrared sensorand the signal input data is provided bythe platform to the BTS App algorithm.The BTS App performs a series ofchecks prior to launching, during thesweep and during the processing ofthe signal to ensure that thetemperature data collected is valid forprocessing. Using this valid collecteddata, the BTS App algorithm	Same
	data, the BTS App algorithmprocesses the sensor data collectedduring the sweep and determines thebody temperature.The displayed temperature is that ofthe temporal artery which isprocessed using a polynomialfunction to approximate a rectaltemperature.	processes the sensor data collectedduring the sweep and determines thebody temperature.The displayed temperature is that ofthe temporal artery which is processedusing a polynomial function toapproximate a rectal temperature.
Specifications
Human bodytemperatureMeasurementRange(Min/MaxAccuracy)	94.1°F-109.4°F (34.5°C-43.0°C)	94.1°F-109.4°F (34.5°C-43.0°C)	Same
LaboratoryAccuracy (Max)	±0.5°F (±0.3°C)	±0.5°F (±0.3°C)	Same
MeasurementSite	Temporal Artery	Temporal Artery	Same
Reference Body RectalSite	Rectal	Rectal	Same
Human bodytemperatureMeasurementRange(Min/MaxAccuracy)	94.1°F-109.4°F (34.5°C-43.0°C)	94.1°F-109.4°F (34.5°C-43.0°C)	Same
Operating Ambient Ranges
Temperature	59.0°F-95.0°F (15.0°C-35.0°C)	59.0°F-95.0°F (15.0°C-35.0°C)	Same
DisplayResolution	0.1°F/0.1°C	0.1°F/0.1°C	Same
TemperatureScales	Degrees °F/°C	Degrees °F/°C	Same

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Summary of Non-Clinical Testing:

The intended use of the subject device and predicate are identical, and their technological characteristics are similar. The subject device is a modification of the predicate device and utilizes the same design and operating principles. The device modifications have been verified and do not raise any new or different questions of safety and effectiveness.

The device demonstrated a laboratory accuracy of ±0.3°C per ISO 80601-2-56. Risk management was conducted in accordance with ISO 14971.

The following testing was conducted to demonstrate that the modifications to the subject device are as safe and effective as the predicate.

Validation Testing .
Results of these tests demonstrate that the functionality, safety, and effectiveness of the subject device are adequate for their intended use, indications for use and support a determination of substantial equivalence.

Summary of Clinical Testing:

Clinical testing was not required for this Special 510(k).

Conclusion:

The proposed modifications to the subject device do not alter the indications for use, intended use, user interface or its core algorithm. There are no differences in the indications for use and intended use between the subject and predicate devices.

One of the technological differences is that pre-measurement checks related to 'Sensor Ambient Temperature', 'Skin temperature', and 'Sensor Window Temperature' values are replaced by binary flags that function similarly to proximity flag check in that a body temperature measurement is only enabled when the appropriate conditions are met. Additionally, the Sensor Ambient Temperature range is being set to hardware specific range instead of a predefined range.

Laboratory accuracy testing and software verification show that the modifications to the software do not raise new or different questions of safety and effectiveness and the device demonstrates substantial equivalence to the predicate device.

The subject device is substantially equivalent to the predicate device, Body Temperature Software (BTS), DEN230050.

Regulation Number and Section

N/A