TREE

When SI (sensor) is closed, power is applied to U2, a dual timer. After a time determined by C2, CI is energized after a predetermined time determined by the value of C5, pin 9 of U2 becomes low, switching off the transistor in the optoisolater, cutting anode current of SCR1 and de-energizing Kl. The system is now reset. Notice that (i6x C2) is less than (R7xC$). The ON time is approximately given by:(R7xC5)-(R6xC2) = Ton  Burglar Alarm With Timed Shutoff Circuit Diagram

This is a simple timed beeper circuit diagram of beeper using 555 timer. This circuit can be employed to energize lights, horn, or other signaling device at any desired interval when the mercury switch is triggered. Since the current handling capability of mercury switch is not so high, an SCR is used to handle current drawn by the 555 timer circuit . Chose the SCR  current rating of 500mA at minimum to safely drive the 555 IC and the relay. The relay is not needed when the current drawn by alarm is less than 200mA, in this case the alarm can be installed to directly replace the relay coil.  Here is the schematic diagram of the circuit. 555-IC Timed Beeper Circuit Diagram