AutoLock is a keypad automatic lock application for Nokia S60 3rd Edition mobile devices like N-Series and E-Series.

Main Features include:

Automatic start-up when the phone is turned on.
Choose your own inactivity time
Runs silently in the background

Download Link- http://fuse.stc.cx/autolock/AutoLock_v1.1_for_S60_3rd_ed.SISX