Headlight Alarm:    Electronic circuit (added 02/05)

Highway Alert Signal Lamp:    (electronic Circuit / Schematic added 10/04)

Hijack Alarm zen22142:    This circuit is designed primarily 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.  (added 10/05)

HiJack Alarm:    This circuit is designed primarily 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.... (added 2/07)

Home Security Project:    (diagram added 6/03)

Infrared Alarm:    This circuits consist of two parts, the first part will transmit a signal, and the second part will detect that signal and trigger a relay. To adjust the circuit, hold down S1 while pointing LED1 at the receiver. Adjust R6 until you hear the relay. You can increase range by using a high output LED for LED1. Bright light will stop the receiver from responding to the transmitter. (added 3/03)

Infra-Red IR Beam Alarm/ Proximity Detector:    This circuit can be used as an Infrared beam barrier as well as a proximity detector.  The circuit uses the very popular Sharp IR module (Vishay module can also be used). The pin nos. shown in the circuit are for the Sharp & VIshay modules. For other modules please refer to their respective datasheets.  The receiver consists of a 555 timer IC working as an oscillator at about 38Khz (also works from 36kHz to 40kHz) which has to be adjusted using the 10K preset. The duty cycle .... (added 10/05)

Intruder Radio Alert System:    (electronic Circuit / Schematic added 10/04)

Keypad Circuit:    (electronic design added 6/07)

Knock Alarm:    (electronic Circuit / Schematic added 10/04)

Light-Sensitive Alarm:    The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to ..... (added 09/05)

Low Voltage Alarm:    NE555 Low Voltage Battery Disconnect Circuit (added 6/06)

Luggage Security System:    (electronic Circuit / Schematic added 10/04)

Melody Generator for Greeting Cards:    This tiny circuit comprising of a single 3 terminal IC UM66 can be built small enough to be placed inside a greeting card and operated off a single 3V flat button cell.  There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. You can either use a 4ohm speaker or a " flat" piezoelectric tweeter like....  (added 10/05)

Mini Alarms :    This is a selection of small self-contained alarm circuits. They have a very low standby current; and are suitable for battery operation.   (added 10/05)

Miniature Loop Alarm mitedu:    (electronic schematic added 8/02)

Miniature loop alarm:    (circuit diagram added 1/07)

Miniature Loop Alarm:    (electronic design added 6/07)

Modular Burglar Alarm circuitsdb:    The Basic Alarm Circuit has an automatic Exit/Entry Zone - an Instant Alarm Zone that will accept both normally-closed and normally-open triggering devices - and an "Always On" 24-hour Personal...(added 05/07)

Modular Burglar Alarm zen22142:    (electronic schematic added 8/02)

Modular Burglar Alarm:    (diagram added 2/07)

Modular Burglar Alarm:    (electronic design added 6/07)

Motorcycle Alarm 3:    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. By adding external relays you can immobilize the bike, flash the lights etc.
(added 10/05)

Motorcycle Alarm 4:    This is a simple easy to build transistor based motorcycle alarm. It's designed to work at 12-volts. But if you change the relay for one with a 6-volt coil it'll protect your "Classic Bike". The standby current is virtually zero so it won't drain your battery. (added 10/05)

Motorcycle Alarm Number 2:    (electronic design added 6/07)

Motorcycle Alarm Number 3:    (electronic design added 6/07)

Motorcycle Alarm Number 4:    (electronic design added 6/07)

Motorcycle Alarm Number 5:    (electronic design added 6/07)

Motorcycle Alarm Number 6:    (electronic design added 6/07)

Motorcycle Alarm:    (diagram added 6/03)

Motorcycle Alarm:    (electronic design added 6/07)

Motorcycle Alarms 5 and 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. (added 10/05)

Motorcyle Alarm 2 :    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. By adding external relays you can immobilize the bike, flash the lights etc. (added 10/05)

N/O: N/C Timed Burglar Alarm :    This is a simple but effective alarm circuit which can reset its self after a time that you select. it has normally open and normally closed triggers which make this circuit very practical. This alarm has normally open and normally closed triggers. It's on a 555 timer so the alarm will reset it's self after a certain amount of time. The time is adjustable....    (added 10/05)

Novel Buzzer zen22142:    (diagram added 6/03)

Novel Buzzer:    (electronic design added 6/07)

Novel Buzzer:    (schematic added 10/06)

Open-door alarm prevents accidental defrosts:    2/1/2007)  EDN Design Ideas  / (added 05/07)    Circuit helps save a lab freezer or temperature chamber's contents.

Optical Proximity Detector:    A "reflector" isolator (A) detects the presence of an object by bouncing light off of it. This technique is useful in circuits that detect when an object is close enough to the sensor (B). (added 3/03))

Oscillating Output Improves System Security:    02/06/03 EDN Design Ideas  /  (added 12/04)  Many electronic-control systems have digital outputs that use transistors. One method of improving the security in these outputs is to use an oscillating signal to represent a logic-high state instead of a fixed voltage level (Figure 1). This type of signal, a dynamic variable, can drive the circuit shown in Figure 2.... (added 09/05)