There is an interesting Android app called "Companion" which works as a companion for those who walk alone. This useful app has been developed by five students of University of Michigan. Using this application your friends / relatives can virtually follow you on your way back home using GPS.
The application uses phone's sensors to detect any abnormal movements like running. In that case the app will ask the user to confirm if he is OK. If nothing is done in 15 seconds, it will go to alert mode with siren like noises and also display a button to call the police. Everything will be notified to the friend / relative on the other side so that he can do the needful.
Have you ever used this application in your Android mobile?