Rain alarm circuit using 555

This Rain alarm circuit uses the water property to conduct electricity. To implement the water sensor we use two pieces of metal, which are placed close enough for a drop of water to let current flow between the metal plates

Car Burglar Alarm using two 555 timers

This is a simple Car Burglar Alarm circuit that uses a dual contact relay and two 555 timers, each of them working as a monostable multivibrator.

The alarm will activate the car horn, approximately 5 seconds after either door is opened and has not been properly closed.

Temperature alarm circuit with 741 operational amplifier

This temperature alarm circuit with operational amplifier activates a relay when the temperature of the place to be controlled exceeds a set level. Useful for an oven temperature control or a cooling system

Over-temperature alarm using operational amplifier.

This over-temperature alarm circuit uses a common semiconductor diode as a temperature sensing element.

This simple alarm with thermostats circuit can be used on places where we must detect overheating. It uses 3 thermostats, and a one, 2 contact, relay

Refrigerator door alarm circuit with two 555 timers

This refrigerator door alarm circuit alerts you when the door has been left open. Very important, because the power consumption increases when this happends. It uses the popular 555 timer IC

Power failure alarm using transformer and relay

This power failure alarm circuit is very simple and is very useful when used with electric ovens, a refrigeration systems or to prevent a thief from cutting off the electrical power because it immediately warns of the problem. It also serves you when the fuses have blown.

Burglar alarm using thyristor and relay

This is a simple Burglar alarm uses a thyristor as the main element and a relay as the output device. The relay can activate a buzzer or a siren.

This light sensitive alarm is very simple and works using, as main components, a transistor, an LDR and a relay.

The alarm activates when the illumination level changes from almost total darkness to a moderately high illumination level. When this happens the alarm is locked and the alarm signal, be it a light or a sound, remains active.

Main Power failure alarm and battery backup Circuit

This Main Power failure alarm circuit tells us when the electricity that powers a system or circuit, is gone.

Over temperature alarm circuit with Thermostat

This alarm circuit uses the 67L080 thermostat (TH) and can be assembled easily, due to the small number of components required.

This shadow detector alarm circuit, detects if there is a difference of lighting between two LDRs, and sends an audible and visual warning.

Circuits that use two LDRs are more reliable than those that use only one.