Laptop Protector
Protect your valuable laptop against theft using this miniature alarm generator. Fixed in-side the laptop case, it will sound a loud alarm when someone tries to...
Intelligent Presence Simulator
However effective a domestic alarm system may be, it`s invariably better if it never goes off, and the best way to ensure this is to make potential burglars thi...
Gated Alarm
Sometimes the need arises for a simple, gated, pulsed alarm. The circuit shown here employs just four components and a piezo sounder and is unlikely to be out-d...
Fridge Door Alarm Schematic 2nd Version
The main purpose of this design was to obviate a small defect of the very popular Fridge Door Alarm circuit, available on this website since 1999 and built by a...
Earth Fault Indicator
The security of many electrical devices depends today on the availability of an earthed mains outlet. We should remember that these are connected to the frame o...
Doorbell MemoryCircuit
If you`re expecting an important visitor but you just have to step out for a moment, an electronic doorbell memory can come in handy so you can see whether some...
Doorbell Cascade
Sometimes you have to do it the hard way, even if doing it the easy way is an option. That is the case here. The intention is to add a second doorbell in parall...
Cat and Dog Repeller
Nowadays, just about every house has an outside lamp with a motion sensor. Such a device eliminates the need to feel your way to the front door, and it apparent...
Vibration Alarm Circuit
This alarm can be very useful in a room or an area that should normally have no movement at all in it. In a totally still room with no movement, no vibration wi...
Tilt Alarm Circuit
This is a circuit where an alarm will go off once the circuit is tilted. Once the circuit is tilted beyond a certain degree, a loud buzzer will go off, alerting...
Sound Alarm Circuit
This is a circuit that will go off if the circuit detects any sound above a certain threshold. Once the circuit detects sound, the alarm goes off alerting us to...
Motion Detector Circuit
This is a circuit which can detect any motion or movement. It`s most common use is to detect a person moving through an area where the motion detector can sense...
Motion Detector Alarm Circuit
This is an alarm circuit which will go off when any motion or movement is detected. Once it detects this motion, the circuit will trigger an alarm buzzer to sou...
Light Alarm Circuit
This is a circuit that will go off once it detects a certain amount of light. Once the light the circuit is exposed to increases to a certain level, a loud buzz...
Remote Doorbell Warning Switch
This circuit will light a lamp at a remote location when the doorbell switch is pressed. This circuit should only be used with the solenoid type doorbells, the ...
The Aurora Alarm
To increase one`s chances of seeing the northern lights, the uncertainties of existing aurora prediction methods can be bypassed by sensing the light from the a...
Im trying to repair a Samsung SCR-3000 DVR COMBO for my security
Repair a Samsung SCR-3000 DVR COMBO for my security system. I`ve replaced 3 capacitors which were obviously blown, and see only one resistor (adjacent to the tr...
I need a circuit diagram and parts list to install a 12v DC
A 12v DC electromagnetic lock with push to lock and push to unlock using my existing LED indicator/switch. The switch should indicate green when unlocked and re...
Laser Beams and 555
A laser trip wire that actuates a camera. An ambient light sensor by Vishay, the TEMT6000 [ datasheet ] from Sparkfun Electronics, acts as an NPN transistor att...
Bathtub water level detector schematic
I poked around till I found an arrangement that worked. Siren circuit: I shorted the reed switch as shown. I removed the power supply and created c.....