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Auto lights-on reminder – Circuit Schematic
Auto lights-on reminder
The alarm is composed of a diode, buzzer, and limiting resistor...
Freezer meltdown alarm – Circuit Schematic
Freezer meltdown alarm
The meltdown is a magnet held to a small stand by ice. A reed switch is below the magnet...
Sun-powered alarm – Circuit Schematic
Sun-powered alarm
Circuit turns on when light (sunlight) strikes photocell. Potentiometer R sets light level at which the alarm sounds...
Latching burglar alarm II – Circuit Schematic
Latching burglar alarm II
Closing the protective circuit (R1 to R2) applies positive voltage to the gate of SCR1 and sounds the alarm...
Boat alarm – Circuit Schematic
Boat alarm
Removing R1 or R2 from the circuit the potential thief breaks a hidden wire that connects R1 to +12 V and R2 to ground)...
Motorcycle or car alarm – Circuit Schematic
Motorcycle or car alarm
Trembler (motion activated) switch sounds the alarm for 5 seconds. Then it goes off...
Latching burglar alarm – Circuit Schematic
Latching burglar alarm
When the protective circuit is interrupted (opened), the alarm sounds...
Auto burglar alarm – Circuit Schematic
Auto burglar alarm
Dome light current-through LI closes reed switch and sounds alarm...
Antitheft device – Circuit Schematic
Antitheft device
Any momentary break in the protective loop or tripping of the normally closed vibration sensor, causes alarm to sound for 20 seconds...
Home security monitor system – Circuit Schematic
Home security monitor system
This circuit provides normally open (NO) and normally closed (NC) contacts SI, S2, and S3 to turn on the alarm after a 30 second delay. S4 and S5 operate instan...
Vehicle security system – Circuit Schematic
Vehicle security system
This alarm gives a 15-20 second exit and entrance delay. After being triggered, the alarm sounds for five minutes and then shuts off...
Security alarm – Circuit Schematic
Security alarm
This alarm features open- and closed-loop detector and automatic alarm shutoff. Offers 15 second exit/entrance delay...
Automotive burglar alarm – Circuit Schematic
Automotive burglar alarm
Alarm triggers on after a 13 second delay and stays on for 1-1 Vfe minutes. Then it resets automatically...
Self-arming alarm – Circuit Schematic
Self-arming alarm
The circuit has a built-in, self-arming feature. The driver turns off the ignition, presses the arm button on theComputalarm, and leaves the car. Within 20 seco...
Adjustable threshold temperature alarm – Circuit Schematic
Adjustable threshold temperature alarm
When Rl increases as temp decreases, the output of IC1 goes positive, turning on Ql. Ql conducts and causes Q2 to conduct, turning on the audible alarm. ...
Temperature alarm – Circuit Schematic
Temperature alarm
The mute pin of this dual audio amplifier is used as the trigger for a one chip high-temperature alarm. ...
Telephone blinker – Circuit Schematic
Telephone blinker
A small neon lamp is triggered into conduction by the telephone's ringing voltage, passes just enough current to activate the LED in optocoupler Ul, which in tu...
High power siren – Circuit Schematic
High power siren
ICla and IClb are wired as a slow astable multivibrator and IClc-ICld are wired as a fast astable. The output of the slow astable modulates the frequency of the...
Siren alarm simulates star trek red alert – Circuit Schematic
Siren alarm simulates star trek red alert
The signal starts at a low frequency, rises for about 1.15 seconds to a high frequency, ceases for about 0.35 seconds, then starts rising again from a low frequ...
Siren system circuit – Circuit Schematic
Siren system circuit
The circuit uses a CA3130 BiMOS op amp as a multivibrator to control the siren's rate. A CA3094 used as a VCO is followed by a CA3082 transistor array used to d...