Fix this tiny White LED lamp near the door lock to locate the keyhole in darkness. It gives sufficient light to lock/unlock the door. It is a short duration timer which turns on the White LED by a press and after a 1 minute it automatically turns off.
Transistor BC547 is used as the LED driver and it switches on the White LED when S1 is pressed. When S1 is pressed for few seconds, C1 charges to full voltage and switch on the transistor. But even if S1 is released, transistor remains on for around 1 minute until the capacitor C1 discharges through R1. Then the White LED turns off .
Assemble the circuit on a small piece of common PCB. Lead-to-lead soldering can also be done since it uses only a few components. Power can be from a 3 volt lithium cell. Paste a piece of Fluorescent paper near the switch to locate it in darkness.