This simple circuit is an extracted circuit board from a discarded quartz timepiece. Most hobbyists might be having one such unit in their junk box. First, disconnect the coil and its fittings, noting the pads that it is connected to. The other components can then be connected across the pads as shown in the circuit diagrams. There are two circuits: manual (shown in Fig. 1) and automatic (shown in Fig. 2).
The circuit (Fig. 1) is powered from a couple of AA cells. Whenever the door is closed, a piece of magnet mounted in the door frame comes close to the reed switch and powers the circuit. When the circuit is powered, LED1 flashes every two seconds. An on/off switch is provided to switch off the unit when it is not required.
As shown in Fig. 2, photo-transistor L14F1 (T1) is added to refrain LED1 from flashing during day time (when there is sufficient light). An on/off switch is provided to switch off the unit when it is not required. This circuit design, if properly mounted, will decorate your door at an amazing low assembling cost. After proper fabrication, fix the complete gadget above your door lock as shown in Fig. 3.