Door-ajar-monitor
The monitor senses an ajar door and, if the situation isn"t corrected within 20 seconds, sounds a beeping alarm. The circuit is controlled by a magnetic reed s...
Transformerless-annunciator
This circuit does not require an output transformer or an output coupling capacitor; the annunciator can easily be turned on or off by a control input voltage d...
Burglar-alarm
This circuit cannot be shut off for 10 to 60 seconds-even if the trip condition is immediately removed. ...
Burglar-alarm
The heart of the circuit is a 555 oscillator /timer, Ul, configured for monostable operation. The output of Ul at pin 3 is tied to the gate of SCRl. As long as...
Easy-auto-alarm
See (a) for the timing information for the alarm circuit in (b). When leaving your vehicle, flip the arming switch and close the door to arm the device. Subseq...
Semiconductor-fail-alarm
False alarms produced by semiconductor failure are impossible with this burglar-alarm circuit equipped with relays. What"s more, the circuit is virtually immun...
Burglar-alarm
The single-chip, burglar -alarm circuit shown uses a dual 556 timer, draws 10 mA of standby current, and generates a pulsing alarm signal that conserves batter...
Auto-alarm
In operation. the alarm circuit allows a 0-47 second time delay, as determined by the Rl/Cl combination, after the switch is armed to allow the vehicle"s motio...
Electronic combination lock
Switches SI through S5 must be operated in rapid sequence to operate the lock. They can be any numbers on a 10-button switch pad...
Power failure alarm
While the power is on, the relay is held open...
Power failure detector
This circuit indicates that a power outage occured for 1, 10, 100, and 500 seconds with the values given for R* and C*...
Power failure alarm
If the power fails, the radio alarm goes on. No loud siren, bell, or whistle...
Rain alarm-door bell
With SI open the circuit functions as a doorbell. With SI closed, rain falling on the sensor will turn on Ql, triggering Q2 and the thyristor and activating the...
Rain alarm
The circuit uses four NAND gates of a 4011 package. In each oscillator, while one gate is configured as a straightforward inverter, the other has one input tha...
Flood alarm
The alarm is built around two audio oscillators, each using two NAND gates. The detection oscillator is gated on by a pair of remote probes. One of the probes i...
Water level alarm
The circuit draws so little current that the shelf-line of the battery is the limiting factor. The only current drawn is the leakage of the transistor. The circ...
Ionization chamber smoke detector II
The smoke alarm signal must be a continuous one rather than pulsating, then the slightly less expensive...
Ionization chamber smoke detector
Battery-operated, ionization chamber smoke detector includes a circuit to generate a unique alarm when the battery reaches the end of its useful life. The circu...
Tone-alert decoder
PLL (Ul) is set with R2 to desired tone frequency. LED lights to indicate lock-up of PLL. Reduce signal level (Rl) and readjust R2 to assure lock-up. Delay is s...
Capacitance operated alarm to foil purse snatchers
As long as touch plates (1) are touched together, the alarm is off. If not held for about 30 seconds, the alarm goes off. The circuit can be disabled with switc...