Siren sounds after wifi drops

Similar to, whenever my router restarts, the siren sounds for a couple of seconds, and then half a minute or so later it does it one more time. Unlike that post, there are no motion sensors, and I haven't tested to see if it happens when the unit is powered on. I was also impatient and did the setup using the DIY approach found on Github.

I'm using one of these 3v relays controlled by pin RX via Home Assistant, which works wonderfully. I followed the instructions in the documentation for wiring an alarm, replacing an existing alarm panel. The one exception is I've connected the COM relay terminal to a U1 pin as, since the board is being powered by the existing alarm panel, there wasn't room for the relay's COM jumper wire.

Don't use the RX pin for this, or your siren is going to sound every time the device reboots.

I suggest using pin D8 with this relay.

Thanks Nate, seems to be working great! Can you (or someone else) explain the why? Thank you!

The RX pin is also used for serial communication over the USB-serial port on the device. At boot/initialization the firmware briefly sets this pin high, which would unintentionally trigger a relay if attached. 

Thanks again!