Smartphone as a Medical Device (SaMD)

Smartphone as a Medical Device (SaMD)

The phone in your pocket is not the medical device. SaMD stands for Software as a Medical Device [1], and the FDA judges medical software on a phone by what that software does, not by the phone it runs on [2]. For anyone who tests with a meter and strips, the strip and meter still do the measuring. The app beside them can be the meter's screen, a logbook, or a regulated device of its own, and those three roles are treated very differently.

What SaMD actually means

The FDA uses the definition written by the International Medical Device Regulators Forum (IMDRF), a voluntary group of device regulators from around the world: SaMD is "software intended to be used for one or more medical purposes that perform these purposes without being part of a hardware medical device" [1]. It is one of three kinds of device-related software. The other two are software inside a medical device, such as a meter's firmware, and software used to make or service a device [1].

The line between them is sharper than we expected. Software that a hardware device needs in order to do its job is not SaMD, even when it is sold separately [3]. Software that connects to a hardware device but isn't needed for that device's medical purpose is SaMD in its own right, and the FDA says it is not an accessory [3].

Why "smartphone" is in the title

The idea of a smartphone becoming a medical device comes from FDA policy. Its guidance on device software functions says oversight "is not determined by the platform": the FDA would not regulate the sale or ordinary consumer use of smartphones or tablets, but it does oversee software that "transforms a mobile platform" into a medical device [2]. The phone changes nothing by itself. The app's intended use decides.

Three roles an app can play next to a meter

The app as the meter's screen

The clearest case of a phone turned into a glucose meter is the original Dario Blood Glucose Monitoring System, which the FDA cleared on December 21, 2015 [4]. Its small meter drew power through the phone's 3.5 mm headphone jack, read a test strip in about six seconds, and showed the result on the phone through the Dario app; the clearance lists the app as the system's display [4]. FDA guidance names exactly this setup, "attachment of a blood glucose strip reader to a mobile platform to function as a glucose meter," as regulated, and points to the same product code (NBW, 21 CFR 862.1345) that covers ordinary over-the-counter meters [2] [4]. Because the system relies on that app to show its result, the app is software in a medical device rather than standalone SaMD [3].

The app as a logbook

Bluetooth meters such as the Contour Next One work the other way around. That meter measures glucose on its own, then sends results over Bluetooth Low Energy to the Contour Diabetes app [5]. FDA guidance lists software that only records blood glucose readings, to share with a clinician or upload to a health record, among functions it does not consider medical devices at all [2]. Software that only transfers, stores or displays device data without changing it is on that list too [2]. Our article on Bluetooth connectivity in meters covers how that data moves.

The app as the medical device

An app becomes a regulated device when it analyzes your numbers and tells you something specific. FDA guidance gives the example of software "that analyzes readings from a blood glucose monitor and alerts the user of readings outside a predetermined range" [2]. Apps that coach people with diabetes toward healthier eating or exercise are a middle case. They may meet the device definition, but the FDA says it doesn't intend to enforce device requirements on them because they pose a low risk [2].

Insulin dose calculators sit firmly on the regulated side. Welldoc's record with the FDA goes back to July 15, 2010, when its DiabetesManager System was cleared through a 510(k) [6]. In 2023 the FDA cleared Welldoc's BlueStar CGM insulin dose calculator, prescription-only software for adults that calculates a bolus insulin dose from the carbohydrates entered and the latest CGM reading and its rate of change [7]. Here's what surprised us: the company's earlier calculator, which stays in the same app, uses fingerstick meter readings, and the 510(k) summary says that version may still be needed when the CGM is unavailable or doesn't match how the user feels [7]. How any calculator is set up, and whether to use one, is a decision for your care team.

How regulators rank SaMD risk

The IMDRF formed its SaMD working group in 2013, with the FDA as chair [1]. The group's risk framework has four categories, I through IV, set by two questions: how serious is the patient's situation (critical, serious or non-serious), and does the software's output treat or diagnose, drive clinical management, or only inform it [8]? Software that treats or diagnoses a critical condition is Category IV, the highest. Software that informs care for a non-serious condition is Category I [8].

The FDA publishes that grid as a "possible" framework [8]. In the US, software that turns a phone into a regulated device still has to comply with the classification for the device it imitates, which for a strip reader means the glucose meter rules [2].

How the rules got here

FDA software policy predates smartphones: the agency drafted a policy on computer and software products in 1989 and withdrew it in 2005 [2]. Its mobile medical app guidance first appeared on September 25, 2013; the version in force as of October 2026 is dated September 28, 2022, and it was revised in 2019 after the 21st Century Cures Act removed some software functions from the legal definition of a device [2]. For meter users, the questions still come back to the 510(k) process covered in our article on regulatory pathways for [test strips](/diabetic-test-strips/regulatory-pathways-510k-for-test-strips/).

What a phone can't do

Every app in this article still gets its glucose number from a strip or a sensor [4] [5] [7]. In February 2024 the FDA warned people not to use smartwatches or smart rings that claim to read glucose without piercing the skin, and said it has not authorized any smartwatch or ring that measures or estimates glucose on its own [9]. The same notice separates those gadgets from smartwatch apps that display data from FDA-authorized devices that do pierce the skin, such as CGMs [9]. If you want to know which role your meter's app plays, the meter's 510(k) summary is a good place to look: Dario's names the app as the display [4], and Contour Next One's describes Bluetooth transfer to a companion app [5].