I've since transitioned from a contact sensor to a motion sensor. I never quite liked how the contact sensor needed to be installed in our community mailbox due to the design that allows mail carriers to open the entire cabinet (all the doors) at once. It worked fine, but I was always a little concerned that the magnet would fall off, or the postal worker might knock the sensor off onto the ground since it needed to stick down below the opening a bit. Probably not very plausible, but I also wanted to try a Yolink hub and there was a good price available on a kit with two motion sensors and a hub. One caveat to using the Yolink motion sensor for this purpose is that it only reports motion active. So when it's joined via D2D with their relay, it can either turn the relay ON or it can turn it OFF. It cannot do both. The answer is to configure their relay for "Pulse Mode", but to do that you have to have their hub. The contact sensor and tilt sensor do not have this requirement since they can be joined to turn the relay ON in one state, and turn it OFF in the other state (i.e. contacted/not contacted or tilted/not tilted.
What I have learned is that the Yolink hubs do not have very good range, versus a device to device connection with their contact sensor. The motion sensor connection to the hub was only able to reach the end of my driveway (around 4 car lenghts), but beyond that it would stop responding. I tried all kinds of orientations and heights, whereas the D2D connection between the Yolink motion sensor and contact sensor reaches half a block away, with the motion sensor attached magnetically to a plate at the back of the community mailbox, which is nested in the middle of rows of other metal boxes. Very impressive range. The Yolink relay isn't mounted up high and didn't need any special orientation. It's just sitting on a shelf a few feet from my garage door, and yet it registers every time the mailbox door is opened. Changing batteries when its time will also be a lot easier since I'll just need to pull the magnetically attached sensor off its metal mounting plate.
I used Amazon's Aeotec Door/Window Sensor 7 Series (ZWA012-A) with an external tilt sense. You can connect a dry contact to that Aeotec. If I have the sensor in the Mailbox, the radio waves won't reach the hub (metal box), so I connected the dry contact sensor to the door. I ran a cable and put the Aeotec in a rubber end in a plastic sleeve with plastic and insulation. I used black zip ties to keep the sleeve in place. Oh, I put a quick connection in the middle of the cable, so when I need to change the batteries, I don't have to touch the sensor itself. I hope this helps.
Thanks for sharing. That's a clever idea and I'm sure it will help someone. Would be absolutley out of the question for a situation like mine, but in situations where the mailbox is within range, and the only caveat is the metal mailbox, then that's a nice solution to the problem. 
My box was within range, but the metal box prevented the single from going anywhere.
Except for when it needs to be repaired or replaced. Then it is our problem.
Yup !
The Visonic MCT-370 and MCT-340E are battery sipping gems.
Zigbee making the trip 50' away THROUGH the steel side of a MailBoss mailbox w/ the magnet tucked away behind the swing door and the module inaccessible to tampering.
Besides the signal RELIABLY carrying through the mailbox wall ...it's the 100 degree F seasonal temperature swings the thing tolerates in that box that amazes me,.
All those considering mounting a device in an unlocked mailbox should consider a couple things,
- doors get left open or otherwise fail introducing weather and theft potential,
- some post-people get freaked out seeing "a device" in the mailbox (and the day of "having the same post-person every day that you can explain this to" seem to be gone)
2a) there may be USPS laws against this by the way, for whatever "law" means anymore - the value of presuming there's nothing in there but junk mail, and feeling safe to just leave it for the day(s) because it's locked....is pretty darn nice.
Getting the locking mailbox has actually been more valuable than putting the sensor inside!
EDIT ADD: I should have just linked the original description of the project:
Similarly, a good old 3326-L motion sensor works remarkably for me. Batteries are lasting for well over a year, and this mailbox is a long way from the nearest Zigbee device. My concern was that anything at the front of the mailbox could be called out by a postal carrier who was having a bad day, and I'd never be able to attach any device to the mailbox again. No complaints about this. [Note: key to success here is a plastic mailbox]
Since everyone is posting pics ...
thanks just found 5 on ebay for 30 bucks.. decide to try them as i have the older looks like the mct-350 but they are the xfinity version.. work fine.. but smaller cr2450 battery lasts afew months in metal mailbox in cold winter.. the larger battery in this one hopefully will be better.
Very similar to my mailbox, except my box is metal and inside a brick enclosure. The motion sensor I used is a Tuya mini that is about 1” diameter. I drilled a 1 1/4” hole in the rear of the metal mailbox and into the brick which the sensor fits into. This worked great for about a month then nothing. Found out the humidity corroded the sensor so I covered a replacement sensor with Saran Wrap. It has been working great for over 6 months.
Iris 3326-L yeah, another amazing little workhorse with long battery life. Didn't someone figure out the permutation of this device? Sad that it is no longer available as it has proven itself for sure.
Now put that sensor in the bell end of a 8" segment of 2" electrical conduit (fits right in the bell connector end), put a PVC cap/plug in that bell, spray paint it the color of one of your trees, stuff some thin plastic mesh in the other open end to keep the bugs out, and PRESTO you have an outdoor motion detector that covers a narrow ~25' forward looking beam.
Just keep it from looking at sun-to-shade-to-sun features that changes rapidly, and pick a tree that doesn't sway. Your mailbox is the model, just shrink it down. It works, and reliably. OK full disclosure...it works but not only for vehicles & people, but every stinking animal passing by... so sometimes two of these looking different ways are necessary with some appropriate Rule logic.
and EVERY waving leaf
