A mobile phone detector can be used to detect mobile phone call. In this video Mr. Atul Pal and Mr. Alok Verma will show you how to make mobie phone detector yourself. This circuit is capable to detect mobile phone in the range of 1 meter.
This can be used in examination halls and many other similar places where use of mobile phones are blocked.
By watching this video you can make a Heating sensor yourself at your home.