41. Door Reed Switch Selection

A reed switch is a magnetically activated switch sealed inside a glass tube. When a magnet comes close enough, the internal reed contacts pull together and close the circuit.

For enclosure door detection, the magnet is mounted on the door and the reed switch on the PCB (or frame). When the door is closed, the magnet is near the switch and the circuit is closed. When the door opens, the magnet moves away and the switch opens.

The controller reads this as a simple digital input: door open or door closed. No mechanical lever, no physical contact with the door — just magnetic proximity.

Required: Glass Body Reed · SPST-NO · 10–20 AT operate range · ≥24VDC · Axial · Through Hole

Go to DigiKey.com → Switches → Magnetic, Reed Switches

Apply these filters:

• Type → Glass Body
• Circuit → SPST-NO
• Operate Range → 10 ~ 20 AT
• Voltage - Switching DC → 24V or higher
• Mounting Type → Through Hole
• Termination Style → Axial
• Part Status → Active

Tip: AT (Ampere-Turns) is the unit for magnetic sensitivity. A lower AT range means the switch activates with a weaker magnet or at a greater distance. 10–20 AT is a common mid-range sensitivity suitable for door gaps of a few millimeters.

The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?

Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide

➡ View Matching Parts — Glass Reed, SPST-NO, 10–20AT, ≥24VDC, Axial