Homemade Motion Detector

Homemade motion detectors are for people with at least some knowledge of electronics. Amateur seismologists might use them simply to detect motion. Most other users attach them to lights, alarms or cameras to trigger those other devices.

Sensor Mechanisms

Motion detection devices use several different kinds of sensors. Some use magnets, lasers, infrared beams or delicate sensors that detect the movement of the air. Sound actuated devices detect air motion, because air motion produces sound.

Detector as Activator

Motion detectors often are integrated with other devices for security. They might activate a porch light or a backyard security light. They might activate an alarm, which is why we sometimes hear those annoying car alarms with oversensitive detectors.

Surveillance

Less benignly, some homemade motion detectors have been used to spy on people. Attaching a motion sensor to a concealed camera or a sound recorder is an example. This is fine if it is designed to prevent a burglary, but an ethical problem if it is used simply to record people without their knowledge.

References

• Discover Circuits: Homemade Geophone Detects Foot Stomp
• Euclid Research: Motion Sensor Reference
• World News: Homemade Laser Motion Sensor
• Nanny Spy Camera: Motion Detector Spy Camera