Indoor letter / mail / post box ZigBee / WiFi door sensor magnet holder

This is my attempt at making my letter box flap (on inside of front door) be intergrated into my Home Assistant setup and not cause damage to anything.

Parts required…

• It uses a cheap AliExpress ZigBee door sensor https://www.aliexpress.com/item/1005007469392459.html, 
• 3x 3M Command Poster Strips (small) https://www.amazon.co.uk/Command-Poster-Hanging-24-Pairs-17024-24ES/dp/B01FIK56Q4 (1 for the magnet arm, 2 for the ZigBee door sensor),
• A small flat magnet (12x1.5mm, I used a random magnet from my desk, but a lot of sizes will fit),
• Some CA (Cyanoacrylate)Glue.

Print Settings…

• I used PLA/PLA+ for the test version with intent of moving to PETG at some point,
• 0.2mm layer height (0.3mm first layer),
• Nozzle Temperature 210°C,
• Bed Temperature 60°C,
• Print in supplied orientation.

Post print…

• Stick on the command strip to the area on the arm (the non-wall side),
• Stick the magnet on with the CA glue,
• Stick the arm to the letter flap (with the "wall" side),
• Put the sensor base onto the door using 2 command strips in a location where the magnet can trigger it (there's a convenient notch where the switch is).
• NB, you may want to put it on the other side of the letter box (my sensor is upside down (does not affect performance),
• Setup a push notification in Home Assistant.

For fun, I set mine (using Pushover) to play the AOL “You've got mail” sound, somewhat ironically!

My doorbell plays the “Doorbell! Doorbell! Doorbell!” sound from the first episode of Rugrats too, but that doesn't have any 3D Printed parts (it's all electronics and MQTT) so no listing on Printables!