Gebildet 5pcs Recessed Wired Security Window Gate Contact Sensor Alarm Magnetic Reed Switch (Black),Magnetic Door Sensor, Normally Closed Magnetic Switch

Good item, works fine, I was a bit worried about the distance for detection, but when I tested these it was almost exactly 15mm distance for detection, which was plenty for me.

Connected these to an ESP32 and then stuck to my door. ESP32 is running ESPHOME which is then connected to Home Assistant. I get instant notifications when the door is open. These reed switches aren't overly sensitive so they do have to be quite close together to actually get the 'closed' signal. They were extremely easy to setup and good value for money.

Used these with a Shelly DCi4 to turn my loft lights on when I open the hatch and it works great. Not the nicest looking so I use them on the inside of the hatch so it can’t be seen.

It's a normally open switch. NO. Not as the ad describes NC. Duh!

These arrived very promptly next day. The five switches and magnets were nicely packaged in a wee plastic box. Screws and sticky pads were included to give alternative fixing methods. The switches have insulated leads of around 30cm in length and at the end the leads are bared and tinned. They seem to work well with the switch operating when the magnet is at a distance of around 10mm. The are described as normally closed but, to me, this was a bit misleading, so I tested them. When there is no magnet the switch is open (non conducting). When the magnet is close the reed switch closes and conducts. I would call that normally open but I suppose it depends on your view of what is normal.

Nicely packed, comes with screws and stick o pads as an option.

Replaced a switch that I had been using for a garage opener. Worked perfectly. Simple, cheap and did the job perfectly. And now I have lots of spares! Recommended.