Car Alarm With Horn As Loudspeaker
An auto horn will work as a speaker of limited audio-frequency range. This circuit uses a 555 timer as a...
Auto Alarm
SI is external key switch. The alarm allows a 0- to 45-s delay after SI is operated before the circuit is armed. During this per...
Automatic Arming Auto Alarm
The circuit automatically turns on when the car is turned off. It gives you a variable time to get out and lock...
Two-Door Annunciator
When the pushbuttons at either door are depressed, this circuit generates a different tone for each door. Tones are ge...
Electronic Door Buzzer
When SI is depressed, an initial positive voltage is placed on C2 and the noninverting terminal of Ul. The circuit o...
Sound-activated-tape-switch
This circuit can cause a cassette recorder to automatically tum on and record when a sound or noise is present. Another use, is when the sound-activated switch...
Electronic-siren
The wailing sound of a siren is generated by a VFO consisting of Q1 and Q2. Capacitor C2 provides the feedback for the oscillator. The frequency of the oscilla...
Capacitive-sensor-alarm
The unit is constructed around a balanced-bridge circuit. using both capacitance and inductance. The bridge consists of capacitors C2 and C3, and the center-ta...
Power-faiwre-alarm
With power ac off, the alarm sounds when S1 is closed on. ...
Ac-power-line-connections-monitor
A continuous glow signifies that everything is normal; a blinking or extinguished neon bulb indicates a broken earth,ground connection, ...
Camera-alarm-trigger
Transistor Ql remains off until the magnetic switch connected to Jl closes. When that happens, the 9 Vis connected through Rl to Ql"S base. Ql turns on, thereb...
Modulation-monitor
Switching diodes are used to fire the neon lamps when negative-peak modulation hits 50. 60, and 100%. To use the circuit, keep an eye on the lamps. ...
Door-opener
The door opener derives its power from a 9-V battery. A momentary-contact switch, 52, is provided in the event that manual opening and closing is required. R...
Bug-detector
This rf detector can locate low-power transmitters (bugs) that are hidden from sight. It can sense the presence of a 1-mW transmitter at 20 feet. which is sens...
Current-monitor-and-alarm
The circuit in Fig. 56-lla lights the signal lamp upon detecting a line current consumption of more than 5 mA, and handles currents of several amperes with app...
Security-door-ajar-alarm
In operation, the TL3019 device will activate, or become low, when a south pole of a magnet comes near the chip face of the device. The example shows five door...
Smoke-detector
This circuit comes from U.S. Patent 3, 778,800, granted to BRK Electronics in Aurora, IL. The circuit provides a smoke detector with an alarm for both smoke an...
Smoke-detector
Use CA3164A BiMOS detector/alarm system. For operation as smoke detector with electromechanical hom (Fig. 40-la), the output of driver at terminal 8 is used. L...
Flood-alarm-or-temperature-monitor
Filtered 15 V de is applied to a series circuit consisting of thermistor R2 and parallel combination of resistors Rl and R3. Transistor Ql acts as a switch who...
Low-battery-detector
Comparator A detects when the supply voltage drops to 4 V and enables comparator B to drive a piezoelectric alarm. ...