Alarms and security circuit diagrams

Hijack Alarm

The first circuit was designed for the situation where a hijacker forces the driver from the vehicle. If a door is opened while the ignition is switched on - the circuit will trip. After a few minutes delay - when the thief is at a safe distance - the alarm will sound and the engine will fail.

Single Zone Alarm

A single zone alarm circuit with entry and exit delay and other facilities.

Two-Zone Intruder Alarm

This is a two-zone alarm - with automatic exit, entry and siren cut-off timers. It can be triggered by the usual types of normally-closed input devices - such as magnetic reed contacts - foil tape - PIRs etc.

Car Alarm and Immobilizer

This circuit features exit and entry delays, an instant alarm zone, an intermittent siren output and automatic reset. By adding external relays you can immobilize the vehicle and flash the lights.

Bidirectional Photoelectric System

Detects and counts inputs and outputs. Suited to control Lamps, Household Appliances etc.

Electronic Door Release

The IC is a quad 2 input "AND" gate, a CMOS 4081. These gates only produce a HIGH output, when BOTH the inputs are HIGH. When the key wired to 'E' is pressed, current through R1 and D1 switchs Q5 on.The relay energises; and Q5 is 'latched on' by R8. Thus, the Alarm is set by pressing a single key,say one of the two non-numeric symbols.

Novel Buzzer

This novel buzzer circuit uses a relay in series with a small audio transformer and speaker.

Personal alarm

Small, portable, anti-bag-snatching unitAlso suitable for doors and windows control

Alarm Power Supply

A 12 Volt power suppiled designed for Ron's Modular Burglar Alarm. However, being a popular supply voltage this circuit will have many other uses as well.

MotorCycle Alarms 5 & 6

These are two - easy to build - relay-based alarms. You can use them to protect your motorcycle - but they have many more applications. If you use relays with 6-volt coils - they'll protect your "Classic Bike". Both alarms are very small. The completed boards occupy about half a cubic-inch - 8 cc. The standby current is zero - so they won't drain your battery.