Multitone generator circuit / Open door indicator using CD4001

This very simple multitone generator circuit has many applications but here it is shown as door indicators, generating a different tone for each door of our house

Shadow detector alarm circuit with two LDRs

This 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.

Temperature Alarm using thermostats

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

Water level alarm. Simple & small alarm with few components. Has small current demand, it can work with a 9V battery for a long time

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 circuit using Thermostat

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

How to make a car temperature alarm?
This car temperature alarm check the car engine temperature and warns us, by means of a sound signal, when the temperature exceeds a seted value

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

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.