Phone Thermometer: How a Thermometer That Plugs Into Your Phone Works

The short answer: a phone thermometer is a small infrared thermometer that plugs into your phone's USB-C port and shows the reading in an app. The phone is its screen, its memory and its power supply, so there is no battery to charge and nothing to pair. TempBuddy is one: it works with iPhone 15 and newer and with Android phones that have a USB-C port, and it reads a forehead in about half a second.

Can a phone measure body temperature on its own?

No. A phone has temperature sensors, but they measure the battery and the processor, not you. Apps that promise to read your temperature through the screen or the camera cannot give a body temperature you can rely on. To measure a fever with a phone you need a thermometer that works with it: either one that plugs into the phone, or one that sends readings to an app over Bluetooth.

How a plug-in phone thermometer works

TempBuddy has an infrared sensor at one end and a USB-C connector at the other. Plug it into the phone, open the free TempBuddy app and hold it 1 to 5 cm (0.4 to 2 in) from the middle of the forehead. The sensor reads the heat given off by the skin and the app turns it into a temperature, shows it on the phone screen with a green, amber or red colour cue, and saves it to the right person.

• No batteries. It draws a tiny amount of power from the phone while it is plugged in.
• No Bluetooth and no pairing. The reading travels down the USB-C connector, so there is nothing to connect or reconnect.
• A big, bright display. The reading appears on the phone screen, which is easier to read in the dark than a small thermometer screen.
• Two modes. Body mode for foreheads. Object mode for a baby bottle, bath water or food, from 0 to 100 °C (32 to 212 °F).

Which phones does a phone thermometer work with?

A plug-in thermometer needs the right port. TempBuddy uses USB-C, so it fits every phone that has one.

Phone	Works with TempBuddy?	Requirement
iPhone 15, 16, 17 and 18 (all USB-C models)	Yes	iOS 17 or later
Android phones with a USB-C port	Yes	Android 7.0 or later
Android phones with a micro-USB port	No	The connector does not fit

Is there a thermometer for iPhone?

Yes. Since the iPhone 15, iPhones use USB-C, so a USB-C thermometer like TempBuddy plugs straight in. Install the free Zanis TempBuddy app from the App Store, plug in and take a reading. The full list of models and the setup steps are in our iPhone thermometer guide.

Is there a thermometer for Android?

Yes. Any Android phone with a USB-C port and Android 7.0 or later works with TempBuddy. The app is free on Google Play. Because the same app runs on both systems, a family with a mix of iPhones and Android phones can share one thermometer.

Phone thermometer or Bluetooth thermometer?

Both send readings to an app. The difference is how they connect and what powers them.

	Plug-in phone thermometer (TempBuddy)	Bluetooth smart thermometer	Standard digital thermometer
Connection	Plugs into the USB-C port	Pairs over Bluetooth	None
Batteries	None, powered by the phone	Required	Required
Display	Your phone screen	Small screen and the app	Small screen
History for each family member	Yes, in the app	Usually, in the app	Last reading only
Works without a phone	No	Usually	Yes

A plug-in thermometer suits people who always have their phone with them and are tired of flat batteries and lost pairings. If you need a thermometer that works with no phone at all, a standard digital one is the better fit.

How to take a reading with a phone thermometer

1. Keep the thermometer and the person in the same room for about 20 minutes first, at a normal indoor temperature.
2. Plug TempBuddy into the phone and open the app. Choose the person you are measuring.
3. Make sure the forehead is clean, dry and uncovered. Move hair and hats out of the way.
4. Hold the sensor 1 to 5 cm from the centre of the forehead and keep it steady for about half a second.
5. Read the result on the screen. It is saved to that person's history with the date and time.
6. If a reading looks unusually high or low, wait a moment and take a second one.

Avoid measuring right after exercise, a bath or a hot drink, or straight after coming in from the cold. Forehead readings usually run a little lower than core temperature, so when you speak to a doctor, say it was a forehead reading.

What the app does

• Family profiles. Every reading saves itself to the right person, so a fever in one child does not get mixed up with another.
• History. A graph of the last 24 hours, 7 days or 30 days shows whether a fever is climbing or settling.
• Symptoms and medication. Log what you gave and when, next to the temperatures.
• A report for the doctor. Export the history as a PDF to share at an appointment.
• Silent Mode. Turns off the scan tone so you can check a sleeping child.

More on this in how to keep a family fever log your doctor can use.

Who a phone thermometer is for, and who it is not for

A good fit for: families who want one thermometer and one history for everyone, parents who check a child at night, people caring for an older parent, and travellers who would rather not pack another gadget with batteries.

Not the right choice for:

• Babies under 3 months. The American Academy of Pediatrics says a rectal reading is the most reliable at this age.¹ Use a phone thermometer from 3 months, or as a second thermometer for quick checks.
• Anyone without a smartphone. The thermometer needs the phone and the app to work.

A thermometer helps you notice and record a fever. It does not diagnose anything. If you are worried about someone's temperature or symptoms, contact a health professional.

Frequently asked questions

Can my phone take my temperature without a thermometer?

No. The temperature sensors inside a phone measure the battery and the processor, not your body. To check for a fever with a phone you need a thermometer that works with it, such as TempBuddy, which plugs into the phone's USB-C port.

Does TempBuddy work with iPhone?

Yes, with every iPhone that has a USB-C port: iPhone 15 and newer, including the iPhone 18 Pro, running iOS 17 or later.

Does TempBuddy work with Android?

Yes, with Android phones that have a USB-C port and run Android 7.0 or later.

Does a phone thermometer need batteries or Bluetooth?

TempBuddy needs neither. It draws a tiny amount of power from the phone while it is plugged in, and the reading travels through the USB-C connector, so there is nothing to charge or pair.

Is the TempBuddy app free?

Yes. The Zanis TempBuddy app is free on the App Store and Google Play. If your app store asks for payment details, that is part of the store's own account setup, not a charge for the app.

How accurate is TempBuddy?

Up to ±0.1 °C (±0.18 °F) in body mode in stable room conditions, as set out in the user manual, and ±0.2 °C (±0.36 °F) in other conditions. Forehead readings usually run a little lower than core temperature, so tell your doctor it was a forehead reading.

Can I use a phone thermometer on a baby?

Use it from 3 months of age. For babies under 3 months, the American Academy of Pediatrics says a rectal reading is the most reliable.

Can it measure a baby bottle or bath water?

Yes. Object mode reads surfaces from 0 to 100 °C (32 to 212 °F), such as a bottle, bath water or food.

Where to buy TempBuddy

TempBuddy is sold on zanis.io and on Amazon. Each one comes with a carry pouch, a 30-day refund and a one-year warranty.

Keep reading

• iPhone thermometer: can your iPhone take your temperature?
• Best contactless thermometer for families: what to look for
• How to take a child's temperature while they sleep
• The best thermometer for grandparents and elderly parents
• TempBuddy support, setup video and user manual

Sources

1. American Academy of Pediatrics, HealthyChildren.org: How to Take a Child's Temperature.
2. TempBuddy ZTP-800 Full User Manual, on our support page.