Plastic Anti-Theft Alarm System, for Home Security, Office Security, Certification : CE Certified

Listing ID #964146

Suitable alarm device for the door & window when its forcibly opened and available at a highly reasonable price of Rs. 390/-, the Anti-Theft Alarm System guards against risk of loss through burglary, theft or criminal damage, which has steadily increased over the years to an extent where electronic intruder detection systems are widely accepted as a necessary and integral part of everyday life for the protection of persons, property and possessions. The reed switch, invented by Dr. W. B. Elwood at Bell Telephone Laboratories in 1936, is an interesting device. It consists of two ferromagnetic and specially shaped contact blades (reeds) positioned in a hermetically sealed glass with a gap between them and in a protective atmosphere. The plated contact surfaces areisolated from the outside environment, which protects the contacts from contamination. Reed switches are available as form A (normally open) and form C (changeover), and are operated using a magnetic field generated by either a permanent magnet or current-carrying coil. The features that make the reed switch a valuable tool include compact size, low weight, quick response time, long life (nominally 50 million operations) and low cost. Some common applications are: reed relays, automotive sensors, robotics sensors, security sensors and
toys.
About the Circuit :
Here we describe the circuit of a 9V battery-operated electronic alarm driver that can be attached to the door leading directly to the house. When the door is opened, the alarm sounds. The circuit is built around resistor R2, a standard bar magnet, reed switch S2, IC CD4093 (N1 through N4), transistor T1 and some discrete components (refer Fig.). NAND gates N1 and N2 are used as an inverter. An oscillator is built around gate N3, resistor R3 and capacitor C2. Gate N4 with resistor R4 and transistor T1 works as a buffer-cum-electromagnetic relay & buzzer driver. When the door is closed, reed switch S2 is in closed state. When the door is opened, the bar magnet moves away from reed switch S2. As a result, the input to gate N1 is high. The low output (pin 3) of gate N1 makes the output of gate N2 high to enable the oscillator. The output of the oscillator circuit is fed to piezobuzzer-driver transistor T1. When the door is opened, the piezobuzzer sounds an alarm alerting that someone is entering the door/widow house area.
Optionally, you can use electromagnetic relay RL1 ( Fig. ) to operate a 230V AC mains operated call-bell or hooter. RL1 energizes/de-energizes at a frequency equal to that of the oscillator. You can lock electromagnetic reed relay in more than one door/window using it in series combination, any switch in between series open it gives alarm.