Iphone 5s tracks your every move. Even when battery is drained

Apple iPhone 5S users take note – even when your phone battery dies, the handset can still track your every move.
This is because when a battery dies, the phone keeps a small amount of power in reserve, meaning its low-energy chip can carry on collecting data from built-in motion sensors.
It can’t track location, however, but it can reveal how many steps a user takes, or establish whether a phone was still being carried around when used with select, third-party apps.

The feature was discovered by Reddit user Glarznak while travelling abroad.
After four days without charge, Glarznak found that when he turned his iPhone back on, the number of steps he had taken during those four days had been recorded on a pedometer app he had installed.

Glarznak wrote: ‘I frequently use Argus [fitness app] to track my steps since it takes advantage of the M7 chip built into the phone.
‘Once I got back from my vacation, and charged the phone, I was surprised to see that Argus displayed a number of steps for the four days that my phone was dead.
‘I'm both incredibly impressed and slightly terrified.’
Apple handsets, as well as other devices, traditionally keep a reserve of power - even when the phone shuts down - in order to maintain certain services and help it boot up when put on charge again.

For example, when a phone battery reaches zero on the display there is, on average, around 5 per cent battery left.

When Apple launched the iPhone 5S, it added what’s called a ‘companion’ chip dubbed M7.

The M7 collects data from sensors including the accelerometer, gyroscope and compasses.
These sensors can detect motion and are used by a variety of apps including fitness trackers, and maps.
It was designed to take this data collection task away from the central processing unit (CPU) to help preserve battery, and speed up the processors.
Each of these sensors are classed as ‘low-energy’, which means the M7 can continue to collect data from them using the battery reserve.  
The M7 does not collect data from the GPS unit, though, because this unit takes up a lot of power and is handled by a separate chip.
This means that although Glarznak’s phone could track his steps, it wasn’t able to track his location.
All the data the M7 collects is encrypted and removed after seven days. It also can't be accessed by Apple's built-in apps - only by apps developed by third parties.
Users also have to allow an app to use motion data, by opting in - it is not a default setting.