How should magnetic sensors be spaced to maintain effectiveness?

• A. 1 inch apart
• B. 3/8 inch to 1 foot apart; wider gaps require stronger magnets
• C. 6 inches apart
• D. No spacing requirement

Answer: (B)

Maintaining reliable magnetic sensing hinges on the magnetic coupling between the magnet and the reed switch. The magnetic field weakens as the gap between them increases, so you need a spacing that keeps the flux strong enough to actuate the switch consistently. The recommended range is 3/8 inch to 1 foot apart. Within this span, the reed switch reliably closes when the door or window is shut, and you avoid nuisance issues from being too close or too far. If you must have a larger gap than that, you’d need a stronger magnet (or additional magnets) to compensate for the loss of flux and maintain effectiveness.