Heatwise: Phone Heat Monitor

Your phone is hot and you want to know whether that is normal. Heatwise answers that, using the only thermal signal iOS actually hands an app, and it refuses to invent a temperature to look impressive.

THE NUMBER OTHER APPS SHOW YOU IS NOT MEASURED

Apple gives no app access to the internal temperature sensors in an iPhone. So when a thermal app prints 41.3 degrees at you, it worked that number out from something else and printed it. One of the popular ones admits exactly this, in a single line at the very bottom of its own description, under nine paragraphs of features.

Heatwise shows you the real thing instead. iOS reports one thermal signal, in four steps, and it is the same signal iOS uses to decide when to cut your phone's speed and dim its screen. Cool, warm, hot, too hot. No degrees, because there are none to be had, and a screen inside the app that names every reading it takes so you can check the claim yourself.

WHAT YOU GET

• A live dial, 0 to 100, that moves as the phone works harder • The exact moment iOS starts holding performance back • Plain answers about what is causing it: charging, sunlight, a thick case, a game, a long drive on Maps • A notification when it gets hot, and one when it cools off with how long the hot spell lasted • Seven days of history with a chart, so you can see whether last Tuesday was worse • Recorded sessions you name yourself, to compare a drive against an hour of gaming • Battery drain per hour while unplugged, worked out over a long enough window to be real

WHY YOUR PHONE GETS HOT

Charging puts heat straight into the battery, and a wireless pad is worse than a cable because some of the power becomes heat before it reaches the cell. A dashboard in summer passes the temperature Apple rates the phone for in minutes. A thick case is insulation. Games, video recording, navigation and AR are the four things that get a phone hot on their own. Heatwise tells you which of these is likely, based on what it can see.

WHAT HEATWISE WILL NOT DO

It will not cool your phone. No app can. There is no fan in there and no software switch that lowers the temperature, so anything with a cooling button is selling you an animation.

It will not watch your phone in the background. iOS suspends apps a few seconds after you leave them, which means no app is monitoring anything while it sits on your home screen. Heatwise reads the phone while it is open and says so, including on the history chart, which counts time watched rather than time passed.

It will not show battery health. iOS does not expose it.

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