Using this circuit diagram can be designed a very simple LED flasher that can be used for example to simulate the existence of car alarms mounted on a vehicle.
This circuit consists on a relaxation oscillator circuit built around transistor T1 that provides repeated pulses, lasting a few milliseconds, Darlington transistor, T2. When contact is closed the LED will lock through T3's.
Circuit power consumption is actually only 2 mA. Resistors R1 and R3 will be resized to compensate for higher tolerances resulting from transistor. Is not recommended that in this circuit to be used, high power LEDs (current peaks must do not exceed 250 mA).