Examples 1-10

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Examples 1-10

Examples 11-20

Examples 21-30

Examples 31-40

Examples 41-50

Examples 51-60

Examples 61-70

This pen prevents ruining shirts by retracting the tip automatically when the pen is clipped into your shirt pocket. The catch that keeps the tip out is actually in the pocket clip. When you pullout on the clip to put it on your shirt, the pin that engages the catch is released causing the tip to retract.


elevator Many Elevators are equipped with an electric eye to prevent doors from shutting on people. They also are equipped with sensors and alarms to prevent operation when overloaded.


brakes Some brake systems utilize permanent magnets to generate power-off braking force.  Current supplied to magnetic coils counter permanent magnetic force to keep the brakes from engaging during normal operation.


smoke Many smoke detectors are designed so they cannot be mounted on the wall until a battery is installed.


gate sensor Retail stores and libraries use "electronic article surveillance" systems to prevent removal of merchandise and books that have not been paid for or checked out.


Pool This device continuously monitors the water level. If the level is too low, a valve opens to add  water to the pool.


stove This Stove burner turns off automatically when pot or pan is removed.


wallet The manufacturer has rigged these wallets to sound an audible beep when a card is absent from the wallet.  While this device would clearly be annoying to some users, for others it would be a big help in remember to replace credit cards after use.


drill The manufacturer has rigged this drill to stop immediately when the bit contacts any grounded or electrically live materials so you can't drill through hidden pipes or wiring.


In China, where electric power has been scarce, hotel rooms are equipped with a room key holder which turns off the power when the key is removed.  This insures no electricity flows to the room while it is vacant.

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