You Have Mail!

If your letterbox is some distance from your house, you will find a monitoring device useful to indicate when new post has arrived. This can take the form of a ...

Whistling Kettle

Most electric kettles do not produce a whistle and just switch off when they have boiled. Fitting a box of electronics directly onto an electric kettle (or even...

Water Level Alert

This circuit will emit an intermittent beep (or will flash a LED) when the water contained into a recipient has reached the desired level. It should be mounted ...

Water AlarmCircuit

Have you ever seen the stairs to one of the upper stories in your house turn into a waterfall Or maybe you`ve come home to find your aquarium fish trying to swi...

Tablet Reminder Uses Watch Module

This device is used as a reminder to take medicine every day. This device actually contains a crystal watch and a 4001 quad 2-input NOR gate with two of the gat...

Smoke Alarm Battery Life Extender

While smoke alarms are quite cheap devices, the cost of 9V batteries quickly exceeds their purchase price. Added to that is the irritation of random beeps from ...

Slave Flash Trigger

Using any camera in a dull or dark environment generally requires the use of supplementary light. This is a standard technique, and even where adequate natural ...

Simple Short-Circuit Detection

This circuit is suitable in every situation where over-current protection is required. Here we give an example from the model train world. Every seasoned model ...

Simple Knock Alarm With Piezo Sensor

This circuit uses a thin piezoelectric sensor to sense the vibrations generated by knocking on a surface; eg, a door or table. Basically, it amplifies and proce...

Simple Combination Lock

This simple combination lock accommodates codes from 1-9 digits long, with the only restriction being that the same digit cannot be used twice. The circuit show...

Simple 6-Input Alarm

This simple alarm circuit was designed for use in a combined garage and rumpus room. It can be assembled on Veroboard and uses just one IC plus a handful of che...

Powerful Security Siren

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-...

Night Alert

Idea of this circuit came to me at midnight when my pet dog started barking continuously on sensing a moving shadow, perhaps that of an intruder. Dogs have a ni...

Multitone Siren

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 ...

Model Railway Short-Circuit Beeper

Short circuits in the tracks, points or wiring are almost inevitable when building or operating a model railway. Although transformers for model systems must be...

Mobile Bug Detector

This handy, pocket-size mobile transmission detector can sense the presence of an activated mobile phone from a distance of one-and-a-half metres. So it can be ...

Midnight Security Light Circuit Schematic

Most thefts happen after midnight hours when people enter the second phase of sleep called paradoxical` sleep. Here is an energy-saving circuit that causes the ...

Mains Supply Failure Alarm

Whenever AC mains supply fails, this circuit alerts you by sounding an alarm. It also provides a backup light to help you find your way to the torch or the gene...

Low Cost Burglar Alarm For Boats

This low-cost burglar alarm employs a 12V strobe light and a truck reversing horn as the visible and audible alarm outputs while the alarm itself is a 12V horn ...

Laser Alarm

This circuit is a laser alarm system like the one we see in various movies. It uses a laser pointer beam to secure your valuables and property. Essentially, whe...