This text is aimed at technicians, hobbyists, and students and provides complete circuit diagrams and building instructions for a wide range of creative sleuthing applications. The designs are fully tested and proven effective in real-world alarm, sensor and security equipment. Among the circuits highlighted are a multi-purpose high-gain amplifier, temperature and pressure sensors, vibration and pyroelectric sensors, smoke and toxic gas detectors, tachometer/speed gauges, a remote video and control system, door and window alarms, motion and impact detectors and tone signalling sensors. Computer interfacing is also covered, with circuits for joystick, trackball, mouse, RS-232 and analog-to-digital interfaces.