I have a 20-year-old Python Garage door opener. Worked fine.

I decided to add an additional "push-button" dry contact relay to the mix so I could operate it with my phone. After unplugging it, I hooked up the wires (22-guage stranded security wire) and tested it and it wouldn't operate.

After other tests, I tried shorting the two screws with a short wire. No joy.

The car (RF) remote works fine, so the safety sensors must be working.

I did this to an identical opener (I have three...) and it worked fine.

Any ideas?

  • Sidenote -- there are special requirements for unattended operation safety in the UL 325 standard, including visible and audible alerting in the garage, as well as a "lockout" if the door doesn't go down after two unattended attempts. See this UL article for more information. Commented May 1, 2021 at 19:56

1 Answer 1


OK, so I finally removed the "dry contact relay" wires, tested them for continuity, and reattached them in reverse. It all worked. My suspicion is that the "dry contact relays" have a "common common", meaning all the relays rely on a joint "common" (even though they all have a separate common terminal....) So, when I connected the relay reverse of how I connected the other garage door opener, I inadvertently ended up "shorting" the second garage door opener. Still not sure why it worked that way, but all's well that ends well, eh?

  • 1
    Sounds like the supposed "relay" isn't a relay at all, but is some sort of electronics which cares about polarity or common. Since your motivation is to control it with your phone, and smart phones can't control normal relays, it sounds like this is some sort of uber-smart gizmo anyway, possibly a "cheap Cheese" non-UL-listed thing (which I don't care about if only low voltage is involved). The cheapos always take shortcuts like using semiconductors instead of mechanicals, or not isolating things which are normally isolated. Commented May 1, 2021 at 20:30
  • The relay pack is a Sonoff 4Ch Pro. Very popular and common, but often used for other purposes, and in different configurations. I have found no docs that say its commons are tied, but lots of docs where tied commons are used. I can't say for sure this is the issue. I may have somehow shorted a terminal to another one, or some other issue. Only low voltage is involved.
    – JimS-CLT
    Commented May 2, 2021 at 20:34
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    Yeah, it's popular because it's cheap, and it's cheap because it doesn't go the extra mile to conform with industrial design standards or certifications. A teardown would tell for sure, but it could also be a solid-state "relay" that does not isolate as much as a mechanical one does. Commented May 2, 2021 at 22:38

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