Physical (not magnetic) wireless door open/close sensor

ronschaeffer · February 19, 2019, 5:22pm

I’m looking for a door open/close sensor which requires physical contact rather than using a magnet ans is battery powered. The use case is for a freezer door which sometimes sticks at a point where it is almost closed–close enough that magnet-based sensors I’ve tried show closed state even though the door is not fully closed. (It’s open enough so that the door seal isn’t tight and so the freezer thaws.)

I’d consider Zigbee, Zwave, 433 or WiFi.

Thanks

123 · February 19, 2019, 5:44pm

You’re looking for a battery-powered RF contact sensor based on a microswitch.

That’s not nearly as common as one based on a reed switch and magnet (as you’ve discovered). You might have to build one from scratch or customize an existing reed/magnet sensor to use a microswitch.

FWIW, I use microswitches to detect the position of deadbolts. However, they’re all hard-wired (to an alarm panel).

ronschaeffer · February 19, 2019, 6:02pm

Thanks for the tips. I’ll build one if I have to but keeping my fingers crossed.

Anyone have other ideas for something off the shelf?

mynameisdaniel · February 20, 2019, 12:56am

Two suggestions:

space the reed sensor from the magnet, such that it only just registers when the door is fully closed (might not be reliable/consistent).
Open up and modify a wireless reed sensor to use a physical switch to connect both ends of the reed sensor instead.

chairstacker · February 20, 2019, 3:51am

I second the 2nd suggestion from @mynameisdaniel.

The ZWave units that I’ve seen so far all have a Reed Switch that would support taking the switch out and putting a physical connection in instead - here’s a photo of a window/door sensor that actually has both, a Reed Switch (2) AND a connector (1):

I use it in my Honeywell alarms system as described here, but the principle is the same.

ronschaeffer · February 20, 2019, 8:41am

Thanks, guys. I’ll look at hack a magnetic door sensor with a micro switch. Does this https://thepihut.com/products/adafruit-micro-switch-w-roller-lever-three-terminal look like a good choice?

123 · February 20, 2019, 3:03pm

Looks almost identical to what I’ve used. It offers the choice of using it as Normally Closed (NC) or Normally Open (NO).

When modifying the reed/magnet sensor, check the reed switch’s state when the magnet is in contact (opened or closed). That’ll determine if you need to use the microswitch in NO or NC mode.

ronschaeffer · February 20, 2019, 4:04pm

Thanks for the advice. I’ll add it to the to-do list!