My friend recently left his iPhone out in the sun while swimming at the pool. When he came back, his iPhone was locked with the message "iPhone needs to cool down before you can use it."

iPhone temperature warning

Neither of us had ever seen this warning before, despite leaving our phones out in the open before.

How hot does an iPhone need to be before displaying a high temperature warning?


TL:DR - Don't leave it in the sun. Especially face up with the black display (and pobssibly bezel) exposed to direct sunlight.

From Apple KB:

Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures

Learn about the operating temperatures and temperature management of iPhone, iPad, and iPod touch (4th generation and later).

Use iOS devices where the ambient temperature is between 0º and 35º C (32º to 95º F). Low- or high-temperature conditions might cause the device to change its behavior to regulate its temperature. Using an iOS device in very cold conditions outside of its operating range might temporarily shorten battery life and could cause the device to turn off. Battery life will return to normal when you bring the device back to higher ambient temperatures. Store the device where the temperature is between -20º and 45º C (-4º to 113º F). Don’t leave the device in your car, because temperatures in parked cars can exceed this range.

Your device might get warm

When you use the device or charge the battery, the device might get warm. You might notice that your device feels warmer in these situations:

  • When you set up your device the first time
  • When you restore from a backup
  • When apps reindex or reanalyze data, like Photos tagging for faces, places, or keywords after a software update

These conditions are normal, and your device will return to a regular temperature when complete.

Here are some of the higher ambient-temperature conditions and activities that might cause the device to change performance and behaviour:

  • Leaving the device in a car on a hot day.
  • Leaving the device in direct sunlight for an extended period of time.
  • Using certain features in hot conditions or direct sunlight for an extended period of time, such as GPS tracking or navigation in a car, or playing a graphics-intensive game.

If your device gets too warm

If the interior temperature of the device exceeds the normal operating range, the device will protect its internal components by attempting to regulate its temperature. If this happens, you might notice these changes:

  • The device stops charging.
  • The display dims or goes black.
  • Cellular radios enter a low-power state. The signal might weaken during this time.
  • The camera flash is temporarily disabled.

Additionally, if you're navigating, the device might show this alert and turn off the display: "Temperature: iPhone needs to cool down." Navigation still provides audible turn-by-turn directions. When approaching a turn, the display will illuminate to guide you through the turn.

If you see a temperature warning screen

If the device exceeds a certain temperature threshold, it will present a temperature warning screen similar to this:

An iPhone showing this message might still be able to make emergency calls.

To resume use of your device as quickly as possible, turn it off, move it to a cooler environment, and allow it to cool down.

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  • This provides a range of recommended temperatures, but does it specify how warm the phone can get before the warning is displayed? – Stevoisiak Jun 25 '17 at 16:50
  • As Apple state "...might cause the device to change its behaviour" then precise temperatures ie exceeding 42.8º C triggers the temperature warning / behaviour are not given. This may be due to external effects such as the surface the phone is laying on being better / worse and a conductor of heat. – Solar Mike Jun 25 '17 at 20:15

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