All 2743 schematics are available on a single page here.

Alarms and security related electronic circuit diagrams / circuit schematics

• Sun - Up Alarm that provides an audible alarm when the sun comes up or a dark area is illuminated
  
• Doorbell for the Deaf
  
• Transistor based single zone intruder alarm
  
• CMOS single zone intruder alarm
  
• Automatic Intruder Alarm - a simple single-zone burglar alarm circuit based on a 4011 quad NAND gate
  
• 5 Zone Alarm Circuit circuit diagram
  
• Ultrasonic Radar Alarm Circuit Diagram
  
• Wireless alarm system based around Nutchip microcontroller
  
• Smartcard controlled relay circuit based around Nutchip microcontroller
  
• RF Pad - combination-controlled, fully customizable radio frequency remote control
  
• Waterpump Safety Guard for fish pond / fish tank
  
• Wailing alarm siren
  
• Refrigerator Door Alarm
  
• Rain alarm / rain detector
  
• Cold activated switch (frost alarm)
  
• Digital combination lock circuit diagram
  
• Perimeter monitor
  
• 5 Zone alarm circuit circuit schematic
  
• Miniature loop alarm
  
• Gate alarm circuit
  
• Touch activated alarm system
  
• Door knob alarm (PDF)
  
• Water seepage alarm (PDF)
  
• Micro-power over temperature alarm (PDF)
  
• Ultrasonic remote control & alarm system
  
• Combination Lock (PIC16F84)
  
• Water level alarm
  
• Home security project
  
• Motorcycle alarm
  
• Enhanced 5 Digit Alarm Keypad
  
• Enhanced 4 Digit Alarm Keypad
  
• RF Alarm
  
• Single Zone Alarm
  
• Water Activated Alarm
  
• Novel Buzzer
  
• Modular Burglar Alarm
  
• Alarm control keypad
  
• Electronic door codelock (PIC16F84)
  
• Frost alarm
  
• Ultrasonic radar alarm
  
• Fridge door Alarm
  
• Emergency Light & Alarm
  
• Door Alarm circuit diagram
  
• Everything-that-moves alarm works by inducing eddy currents in living beings
  
• Electronic locker digital combination lock circuit diagram
  
• Gate alarm
  
• Circuit diagram for 5 Zone Alarm System
  
• Miniature Loop Alarm
  
• Modular Burglar Alarm
  
• Water Activated Alarm
  
• Enhanced 5 Digit Alarm Keypad
  
• Enhanced 4 Digit Alarm Keypad
  
• Automatic Intruder Alarm
  
• Single Zone CMOS Alarm
  
• Travel Touch Alarm
  
• 4 Photo-Detector circuit with delayed release and bipolar output
  
• Digital Keypad Combination Lock
  
• Wire Loop Alarm using 4001UBE Quad NOR Gate
  
• Digital combination lock using pair of CD4013 CMOS chips
  
• Proximity detector (uses human body capacitance)
  
• Build an iButton electronic lock based around a AT91C2051 microcontroller (includes ASM source code)
  
• Circuit diagram for basic alarm with delayed trigger
  
• Wireless alarm FM transmitter module
  
• Fuse or line monitor that will check the status of up to six fuses including a PCB layout
  
• RFID Access Control System based on an Arduino
  
• Arduino Based Security / Automation Sensors
  
• Motorcycle Alarm
  
• Car Alarm and Immobilizer
  
• Car Hijack Alarm
  
• Motorcycle Alarm Number 2
  
• Motorcycle Alarm Number 3
  
• Motorcycle Alarm Number 4
  
• Motorcycle Alarm Number 5 & 6
  
• Auto Burglar Alarm
  
• LPG leakage alarm using SEN-1327 gas sensor module (detects 4 other dangerous gases)
  
• Sensitive Optical Burglar Alarm
  
• Sound operated music bell using 555 timer