Touch the sensor ... the alarm circuit is enabled by T1 and T2. Transistors T3and T4 form a complimentary pair amplifier, with positive feedback (regeneration) provided to the base of first transistor ...

Simple Sound ... As the circuit has no critical adjustment points it is immediately ready for real-world applications. The acoustic sensor in the circuit is a standard omni-directional foil electret ...

Ring's $199 Z-Wave-enabled Alarm Security Kit is so simple you might overlook it at first. The system includes a base station, a keypad, a door/window sensor ... alarm will sound if unexpected ...