According to an urban myth that has circulated in the UK for several years, dialling 999 on your mobile phone then immediately hanging up will instantly recharge your phone battery.
Of course, the claim is utter nonsense. Dialling 999 or any other number will certainly not boost your phone battery.
Unfortunately, this myth is potentially more dangerous and damaging than other silly phone charging hoaxes. 999 is the emergency number in the UK, so the hoax is causing ongoing problems for UK authorities. An August 2013 Mirror Online article notes:
Mobile users have been urged to ignore an urban myth that claims dialling 999 charges their phone’s battery. Derbyshire Police said they’d received several emergency calls that turned out to be from people believing their phone would be charged.
Unfortunately, police have to waste time following up such calls in case they are legitimate.
Hoax calls can tie up the emergency number and could potentially slow responses to real emergencies. Calling your country’s emergency number for any reason other than a genuine emergency is irresponsible. And, making a prank call to emergency services is a criminal offence in the UK and many other jurisdictions.
If this absurd hoax comes your way, be sure to let the sender know that the claims are untrue and potentially dangerous.