Waterproof contact sensor or ideas for mailbox?

I wouldnt reccomend that. I used this for my bathroom Window and had to put some foam between my sensor and the window because it was made out of metal. The metal doesn’t just mess with signal it makes devices not truelly work. It freaks out if either strip is straight on metal and doesn’t give correct reading. Just a little warning. It says on manual too that you shouldn’t put it directly on metal.

Well I have combined a few methods and took it one step further. Since I already have the Dakota 2500 system for my motion outside, that hooks to a few motion contacts (DWZWAVE2-ECO) and to the Dakota receiver, I wanted to use the same concept for my mailbox since their transmitters has distance of 1/4 mile. So what I have done is use the UT-2500 for my transmitter and hook that to a Ademco 945T-WH magnet contact for the mailbox. Then same concept for the motion I hook the Dakota 2500 receiver to a DWZWAVE2-ECO. My mailbox is in a stucco enclosure. My mailbox is about 300 feet from the receiver and I have no problems with getting the alert that the mailbox is open.

My mailbox is not only metal but its roughly 50 feet away from my house.

well this setup will work then I have to go through a metal box that is surrounded by Stucco and 300ft from the house. no problems at all

Liquid insulating tape, its ace for waterproofing my contacts and motion sensors.