Precious home appliance anti-theft alarm

This valuable home appliance anti-theft alarm has the characteristics of small size and loud sound. It is suitable for use in homes, hotels, offices, etc.

How it works

       
The circuit principle is shown in Figure 1. SCR, R1 and AN form a thyristor trigger switch circuit; IC1, R2, VT1, VT2 and BL form a simulated siren circuit. Usually, AN is pressed by household appliances, causing its two normally closed contacts to be disconnected, SCR is blocked without a trigger signal, and the alarm does not work. When the household appliance is lifted, the two contacts of AN automatically close, the trigger end of SCR obtains a trigger signal from the positive pole of the power supply through R1, SCR is turned on, IC1 is powered on, and the siren signal output from its output end is amplified by VT1 and VT2, driving the speaker to emit a loud alarm sound. At this time, even if the household appliance is put back to its original place or AN is destroyed, the alarm sound cannot be stopped. The alarm can only be released when the owner turns on the switch S, which is installed together with the alarm and difficult for others to find.

Component selection and production

The components list is shown in the table below.
 

The alarm part can be installed in a small plastic box and placed in a place where the alarm sound can be easily heard (such as a duty room, etc.). Use a double-strand thin wire to lead the AN to the place where the home appliance is placed, and cleverly place the AN on a desktop, countertop or TV cabinet, etc., to ensure that the AN can operate correctly.