Samir has done a great job making this new application for the Symbian S60 phones. It is called nAlertMe and is available for download at his site – AikonLab.

The application has this functionality:
1. Define a custom alarm deactivation sequence.
2. Activate the alarm.
3. Put your phone somewhere.
4. When someone picks up the phone and tries to use it without using the deactivation sequence (which is the unique one you generated in step 1, and involves tilting your phone left and right), a loud alarm goes on in a few seconds, so you will know that someone is using your phone without your permission.

Here is a nice preview video of the functionality of this application: