Tag Archives: alarm

Multitone Siren

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This multi-tone siren is useful for burglar alarms, reverse horns, etc. It produces five different audio tones and is much more ear-catching than a single-tone siren. The circuit is built around popular CMOS oscillator-cum-divider IC 4060 and small audio amplifier LM386. IC 4060 is used as the mult-itone generator. A… Read more »

Mini Alarm

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Suitable for doors & windows, Portable anti-bag-snatching unit This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means… Read more »

Powerful Security Siren

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Simple circuit – No ICs required, 12V Battery operation This circuit was requested by several correspondents. Its purpose was to obtain more power than the siren circuit already available on this website (One-IC two-tones Siren) and to avoid the use of ICs. A complementary transistor pair (Q2 & Q3) is… Read more »

Door KnocK Alarm With Timer

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This low-cost circuit uses the piezoelectric element of a piezobuzzer as the input sensor. The piezoelectric element plate is fixed at the centre of the door wing by using a cello tape. Apply a small quantity of adhesive at the edges between the plate and the door. Extend wires about… Read more »

Non-Contact Power Monitor

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Here is a simple non-contact AC power monitor for home appliances and laboratory equipment that should remain continuously switched-on. A fuse failure or power breakdown in the equipment going unnoticed may cause irreparable loss. The monitor sounds an alarm on detecting power failure to the equipment. The circuit is built… Read more »

Under-Over-Voltage Beep for Manual Stabiliser

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Manual stabilisers are still popular because of their simple construction, low cost, and high reliability due to the absence of any relays while covering a wide range of mains AC voltages compared to that handled by automatic voltage stabilisers. These are used mostly in homes and in business centres for… Read more »