Your iPhone’s lock screen shows you all kinds of useful information and buttons: date and time, notifications, playback controls when listening to music. In some cases, the iPhone lock screen only shows icons like batteries of different colors or a thermometer.
Each icon provides you with useful information, if you know what it means. It is important to understand what these icons mean and what to do when you see them. At least in one case, it can save your iPhone from serious damage.
Red battery icon: Recharge time
You may see an ominous red battery icon on your iPhone’s lock screen if it’s been a while since you last charged your iPhone (see this article for tips on how to make your battery last longer). If you do, your iPhone is telling you that its battery is low and needs to be recharged. The charging cable icon below the red battery icon is another indication that you need to plug in your iPhone.
The iPhone keeps going while showing the red battery icon on the lock screen, but it’s hard to tell how much life it has left (unless you’re looking at battery life in percent). It is better not to tempt fate. Recharge your phone as soon as you can.
If you can’t charge it right away, you should try low power mode to extend battery life. More on that in the next section.
If you’re always on the go and can’t always charge your phone, it might be worth buying a portable USB battery or battery case to make sure you don’t run out of power.
Orange battery icon: Low power mode
You won’t see this icon on your lock screen, but sometimes the battery icon in the top corner of your iPhone’s home screen turns orange. This indicates that your phone is operating in low power mode.
Low Power Mode is a feature in iOS 9 onwards that extends battery life for a few more hours (Apple says it adds up to 3 hours of usage). Learn more about Low Power Mode and how to use it in this article.
Green battery icon: Charging
Seeing a green battery icon on your lock screen or in the top corner of your screen is good news. It means that your iPhone battery is charging. If you see that icon, you probably know your iPhone is connected. Still, it’s nice to know to look for it in case you’re trying to load it and something isn’t working properly.
Red thermometer icon: iPhone is too hot
It’s not common to see a red thermometer icon on your lock screen. It’s also a bit scary as your iPhone won’t work while the thermometer is present. A message on the screen tells you that the phone is too hot and needs to cool down before you can use it.
This is a serious warning. This means that the internal temperature of your phone has risen so high that the hardware could be damaged (in fact, overheating has been linked to cases of exploding iPhones). Several things can cause this to happen, including leaving a phone in a hot car or a battery-related malfunction.
When this happens, the iPhone protects itself, according to Apple, by turning off features that could cause problems. This includes automatically stopping charging, dimming or turning off the screen, reducing the strength of the connection to phone company networks, and disabling the camera flash.
If you see the thermometer icon, immediately place your iPhone in a cooler environment. Then turn it off and wait for it to cool down before trying to restart it. If you’ve tried these steps and let your phone cool down for a long time but still see the thermometer warning, you should contact Apple for support.