Can a Phone App Check Your Blood Sugar?

No. A normal smartphone or phone camera cannot directly measure blood glucose by itself. Blood sugar is measured by a glucose meter using a drop of blood on a test strip, or by a continuous glucose monitor (CGM) with a sensor placed under the skin. A phone has neither. Apps that claim to read your glucose through the camera, the flashlight, a fingerprint sensor or the screen are not measuring anything. The FDA has already warned consumers not to use smartwatches or smart rings that claim to measure blood glucose without piercing the skin, and the same reasoning applies to a phone.

What a phone can do is display and store readings that come from a real measuring device — and that is useful. This article separates the two, explains how glucose is actually measured, and describes what a tracking app like DiabetLog does and, just as importantly, does not do.

How blood glucose is actually measured

There are two established ways to measure glucose at home, and both involve a regulated medical device.

A blood glucose meter

The FDA describes a blood glucose monitoring device as a handheld meter with test strips that measures the amount of glucose in a small sample of your blood. You prick a fingertip with a lancet, place the drop on a disposable strip, and the strip's chemicals react with the glucose; the meter measures that reaction electrically or optically and shows a number. In the US the result is reported in mg/dL.

A continuous glucose monitor (CGM)

The NIDDK explains that a CGM uses a tiny sensor inserted under the skin — often on the belly or arm — to estimate the glucose level in the fluid between your cells every few minutes. The CDC notes that if you use a CGM you will still need to test with a blood sugar meter to help make sure the CGM readings are accurate.

In both cases something has to reach blood or interstitial fluid: a test strip or a sensor. A camera pointed at a finger does not.

What about apps that claim to use the camera, flashlight or fingerprint?

In February 2024 the FDA issued a safety communication about smartwatches and smart rings that claim to measure blood glucose without piercing the skin. Its position is unambiguous: the FDA “has not authorized, cleared, or approved any smartwatch or smart ring that is intended to measure or estimate blood glucose values on its own,” these devices “do not directly test blood glucose levels,” and consumers should not buy or use them.

The warning is specifically about watches and rings, but the reasoning applies directly to phone apps making the same promise. The FDA explains why the stakes are high: for people with diabetes, inaccurate glucose measurements can lead to errors in diabetes management, including taking the wrong dose of insulin or other medicines that rapidly lower glucose — which can lead to dangerously low blood sugar within hours.

A few signals that an app is making a claim it cannot back up:

• It says you can measure glucose “without a meter”, “without test strips” or “no finger prick” using only the phone.
• It asks you to place a finger over the camera or flashlight, press the screen, or take a photo of your eye or skin to get a glucose value.
• It presents a number with no connection to any FDA-authorized meter or CGM.

The FDA distinguishes these from legitimate apps that display data from FDA-authorized measuring devices. That distinction — the device measures, the app shows and stores — is the whole point of the next section. If your care depends on accurate readings, the FDA recommends talking to your health care provider about an appropriate authorized device.

Measurement vs tracking: what phones are good at

A phone is a terrible glucose meter and an excellent logbook. The FDA lists the ability to store results and to transmit data to a computer, mobile phone or cloud service among the features to consider when choosing a meter; the CDC notes that some meters use an app on your phone to track your levels, and that a written record works too. The NIDDK says to keep a record of each self-check — date, time, result, and notes such as food or activity — and that you can use a chart or a smartphone app to do it.

So the honest job description for a glucose tracking app is:

• Manual logging — you type in the reading from your meter, with the time of day and context.
• History and charts — the entries build into a timeline you can scan for patterns.
• A target range — you enter the range your care team gave you, and the app shows which readings fell inside or outside it.
• Reminders — nudges at the check times in your schedule.
• Reports — a clean summary to bring or send to your doctor.

None of that requires the phone to measure anything. It requires you to measure with a real device and the app to keep the record well.

What DiabetLog does — and does not — do

What DiabetLog does do:

• Logs readings in seconds, tagged with the time of day and a context such as fasting.
• Shows charts, statistics and trends of your history.
• Lets you enter a custom target range — the one from your care team — and shows which readings were in range, too high or too low.
• Sends reminders at the times you choose.
• Creates PDF doctor reports (Premium) that you can share before an appointment.
• Syncs with Apple Health on iPhone, optionally.
• Keeps everything on your device. No account, no server, no upload unless you choose to share a report.

It is available for iPhone and iPad and for Android, and it is free to download. If you were searching for a free app to check blood sugar, this is the honest version of that: a free app to record blood sugar, paired with the meter your pharmacy or care team provides.

So what do you actually need?

1. A blood glucose meter or a CGM. The FDA suggests your health care provider may have a recommendation based on your needs, and warns against using previously owned test strips or strips not authorized for sale in the US.
2. A way to record the readings. A paper log — the free printable blood sugar log sheet works — or a logging app like DiabetLog.
3. A schedule and a target range from your healthcare professional. The CDC notes your doctor will tell you when and how often to check. Our article on when people with type 2 diabetes are asked to check explains the vocabulary.
4. Consistency in the unit. If you ever see a value in mmol/L, the mmol/L to mg/dL converter translates it before you write it down.

The phone's role in all of this is the second item. Used that way, it is genuinely helpful — and it never pretends to be the first.