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13 Color LED Rainbow
4 Digit Keypad
5 Zone Alarm Circuit
A CMOS 4060 Burglar Alarm - This is a single zone alarm, with automatic exit, entry and siren cut-off timers. It will accommodate all the usual types of normally-closed input devices, such as magnetic reed contacts, foil tape, PIRs etc. But it's easy to add a normally-open trigger.
A CMOS Based Motorcycle Alarm  - This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition..
A CMOS Based Single Zone Alarm - This circuit features automatic Exit/Entry delays, timed Bell Cut-off and System Reset. It has provision for normally-open and normally-closed switches and will accommodate the usual input devices (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia Sensors)
A CMOS Based Vehicle Anti-Theft Alarm - This car alarm 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.
A CMOS Single Zone Intruder Alarm - This circuit features automatic Exit and Entry delays, timed bell cut-off, and system reset. It has provision for normally-open and normally-closed switches, and will suit all of the usual input devices (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia-Sensors
A One-Time-Only Burglar Alarm - When this alarm is activated its Siren will sound once, for up to 20-minutes. Then it will switch off and remain off. The basic circuit has a single zone with independently adjustable Exit and Entry delays. This will be adequate in many situations. However, there's also range of Expansion Modules. These will allow you to add any number of Instant Zones, Tamper Zones and Personal Attack Zones to your system.
A Shed/ Garage Alarm - This is a basic single-zone burglar alarm circuit. Its features include automatic Exit and Entry delays. It has an extremely small standby current. This makes it ideal for battery-powered operation. Use it in your caravan, mobile home, lock-up, or anywhere mains power is not available.
A Simple Fire-Door Alarm  - This circuit will let you know when something that should be kept closed, has in fact been left open. Attach it to a Fire-Door. It will allow you to pass through the door as usual. However, if it's left open for more than 30-seconds or so, the buzzer will sound.
A Simple Shop-Door Alarm  - Attach this circuit to the door of an unattended shop, or reception area, and the sound of the buzzer will tell you when you have a customer. Add a siren, and it becomes a simple intruder alarm.
A Simple Transistor Based Motorcycle Alarm - This is an even simpler transistor based motorcycle alarm. The circuit features a timed output and automatic reset. It can be operated manually using a key-switch or a hidden switch. By adding an external relay, it will set itself automatically, and/or immobilize the machine, every time you turn-off the ignition. It's easily adapted for a 6-volt system, so it will protect your "Classic Bike"
A Simpler CMOS Single Zone Alarm - This circuit features automatic Exit/Entry delays, timed Bell Cut-off and System Reset. It will accommodate the usual normally-closed input devices (Magnetic Reed contacts, Micro Switches, Foil Tape and PIRs). And, with a simple modification, a normally-open trigger may be added.
A Transistor Based Single Zone Alarm - The circuit features automatic Exit and Entry delays, timed Bell Cut-off and System Reset. It has provision for normally-open and normally-closed switches and will suit the usual input devices (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia Sensors). 
Alarm control keypad
An Enhanced Shed/ Garage Alarm  - This is an enhanced version of the simple Garage/Shed Alarm. The Entry and Exit delays have been increased to about 30-seconds, and I've added a timed Siren cut-off and automatic Reset. I've also replaced the LED with an entry Buzzer. These enhancements mean that the new version will have a much wider application.
An Expandable Multi-Zone Modular Burglar Alarm - This circuit features automatic Exit and Entry delays and a timed Bell Cut-off. It has provision for both normally-closed and normally-open contacts, and a 24-hour Personal Attack/Tamper zone. By using the Expansion Modules, you can add as many zones as you require; some or all of which may be the inertia (shock) sensor type.
An Expandable SCR Based Burglar Alarm - This is a simple SCR based burglar alarm circuit. Its features include automatic Exit and Entry delays, together with a timed Bell Cut-off and Reset. The basic alarm has a single zone. This will be adequate in many situations. However, the modular design means that you can add as many zones as you like to the system. Details of a Four-Zone expansion module are provided.
An Expandable Transistor Based Burglar Alarm - This transistor based alarm features automatic Exit and Entry delays, together with a timed Bell Cut-off and system Reset. Along with the Exit/Entry zone, the basic alarm board has one Instant Zone. This will be adequate in many situations. However, the modular design means that it's easy to add as many zones as you like to the system. Details of a Four-Zone expansion module are provided.
An SCR Based Burglar Alarm
Analog Video Router - Intersil Application Block Diagram
Anti Theft Motorcycle Alarm
Anti-Bag-Snatching Alarm
Anti-Theft Alarm for Bikes
Anti-Theft Security for Car Audios
Auto Burglar Alarm (Randy Linscott) - This alarm circuit is based on two 555 timers. The alarm will sound your car horn if anyone opens the car door while the circuit is armed. The timers will allow you to leave the car without sounding the horn. To turn the circuit on S1 must be closed.
Automatic Door Opener with PIC12c508 - This circuit can be used to operate an electric strike or an electromagnetic lock on a door. It is not  door being opened/closed, but a small electromagnetic strike which unlocks  door…
Automatic Intruder Alarm
Automatic Room Lights - An ordinary automatic room power control circuit has only one light sensor. So when a person enters  room it gets one pulse and  lights come ‘on.’ When  person goes out it gets anor pulse and  lights go ‘off.’ But what happens when two persons enter  room, one after  or? It gets two pulses and  lights remain in ‘off’
Battery-Powered One-Time-Only Burglar Alarm - This is a single zone alarm, with independently adjustable Exit, Entry and Siren Cut-Off timers. When the alarm is activated its Siren will sound once, for up to 20-minutes. Then it will switch off and remain off. If you wish, you can use a mains power supply. But the extremely low standby current makes battery power a realistic option.
Build yourself a Witness Camera - The Witness Camera is an automated, self-recording surveillance camera, that uses a gigabyte-class flash card as recording media. I designed the Witnesscam because available surveillance solutions were too expensive or impractical for home use. I built the system from a VGA CMOS colour camera, a passive-infrared (PIR) movement sensor, an ATmega32 processor, and a 1GB SD-card.
CMOS 4060 Burglar Alarm - This is a single zone alarm, with automatic exit, entry and siren cut-off timers. It will accommodate all the usual types of normally-closed input devices, such as magnetic reed contacts, foil tape, PIRs etc. But it's easy to add a normally-open trigger.
CMOS Based Motorcycle Alarm - This circuit features automatic Exit/Entry delays, timed Bell Cut-off and System Reset. It has provision for normally-open and normally-closed switches and will accommodate the usual input devices (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia Sensors).
CMOS Based Vehicle Anti-Theft Alarm - This car alarm 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.
Combination Digital Lock - A multiple input combination lock using CMOS counter IC's. Flexibility and code change is allowed by changing output connections.
Combination Lock PIC16F84
Combination Lock-Digital
Cut Phone Line Detector (Aaron Cake) - Can be used to alarm security system
Cut Phone Line Detector (Tony van Roon)
DayLight Alarm - The circuit presented here wakes you up with a loud alarm at the break of the daylight. Once again the 555 timer is used here. It is working as an astable multivibrator at a frequency of about 1kHz.  The circuit's operation can be explained as follows: When no light falls on the LDR, the transistor is pulled high by the variable resistor.
Digital Combination Lock
Digital Electronic Lock (Bill Bowden) - The digital lock shown below uses 4 common logic ICs to allow controlling a relay by entering a 4 digit number on a keypad. The first 4 outputs from the CD4017 decade counter (pins 3,2,4,7) are gated.
Door/Window Sensor Resists Tampering - EDN-Design Ideas: The simple, inexpensive circuit in Figure 1 detects a failure (or deliberate tampering) on lines connected to normally closed switch sensors. For example, common door interlocks and door/window sensors consist of normally open or normally closed magnetic reed switches. Depending on the monitoring configuration, an open or short on a line may go undetected, thus preventing alarm activation. Embedding a resistor in a normally closed sensor and using bipolar dc power supplies produces the balanced configuration in Figure 1. A short or open on a line (or sensor activation) produces a net positive or negative voltage at the input of the Q1-Q2 pair.
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