Before you start to retrace your steps through town, check to see if your handset is nearby-it could have just fallen down the side of the chair.
Whistle Phone Finder is a free Android app that transforms your phone into a modern version of a whistle-activated keyring. It can be installed on just about any Android device-no need for root-and will help to reunite you with your handset in a tuneful way.
Fire up the app and check the Enable Whistle Phone Finder option, and then tap Whistle Sensitivity Setup to choose how easily the app should be set off-you may need to experiment with this to see what works best for your phone-and then choose a sound. It's a good idea to enable the Use High Audio Volume option as well as it makes your phone easier to hear.
The app is active whenever your phone is in sleep mode. Next time you need to locate it, just whistle and your chosen sound will be played back at you. It does not matter if your phone is in silent mode, the app will still work.
You might not want to enable the app all of the time, as constantly listening out for whistle will take its toll on some batteries. If it is too much of a drain for your phone, consider enabling it just when you visit places where there is a risk of phone loss.
Keep in mind that in order for Whistle Phone Finder to work you need to be relatively near your phone-at least in the same room. I had some problems when testing it in loud environments, but to help find out whether your phone is in the car or down the side of the sofa, it's perfect!