Wonder why your smartphone battery runs down, even when you aren't using the device? Chances are, it's not getting enough sleep.

Because smartphone functions are energy hogs, reducing battery life in normal operations, manufacturers have aggressively built in “sleep” functions. When the device detects no activity, the smartphone goes into sleep mode to save power.

But it's not entirely asleep. Various functions need to run in the background, such as checking with the email server to see if any new messages have arrived. While the phone is sleeping, an app springs into action every now and then and wakes up the phone just to see if it needs to perform a function.

And therein lies the problem. Under normal circumstances the app will do its job, then let the phone go back to sleep. But Charlie Hu, a Purdue University professor of electrical and computer engineering, says sometimes there's a glitch in the software and the phone stays awake.