I made my mailbox smart by adding a fingerprint lock and two zigbee contact sensors for automatically setting and resetting the mail status in Home Assistant.

When the flap is opened
– first zigbee contact sensor is activated
– the mail boolean is set to true and “New mail” is displayed next to the mailbox icon in my Home Assistant app.
– I receive a notification on my phone and via my Sonos One speakers

When the door/hatch is opened
– the second zigbee contact sensor is activated
– the mail boolean is set to false and “Empty” is displayed next to the mailbox icon in my Home Assistant app.

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I use these Aeotec/SmartThings zigbee contact sensors due to their longer range than Aqara (in my mailbox-testing): https://aeotec.com/products/aeotec-multipurpose-sensor/

I use a fingerprint lock which is stated to unlock 3000 times on a single charge (in my testing it lasted a few months): https://www.aliexpress.com/item/1005004745433425.html (I use the 36/20mm version)

The fingerprint lock charges via micro usb on the front.

Battery free (but still keyless) alternative to fingerprint lock: https://a.aliexpress.com/_m0q0zG6

If your mailbox cannot reach your zigbee network, then check out this cool project using LoRa: https://www.youtube.com/watch?v=gf1WWKyEnbg&t=0s&ab_channel=PricelessToolkit

UPDATE

Smart mailbox update: The mailbox fingerprint sensor survived the freezing winter, snow and the rainest months recorded in Denmark in decades, but the tiny battery now lasts less than two weeks which is not quite enough to be practical.

I have disassembled the fingerprint lock and considered a solution with a bigger external battery inside the mailbox, but feeding a wire through to the back of the lock and through mailbox is not easy since it needs to be able to rotate but not freely. A better (and slimmer) solution might be to only have the fingerprint-sensor on the outside and have a different locking mechanism on the inside. Any ideas are welcome.

In the meantime I have installed this combination lock (https://a.aliexpress.com/_Ez3cVS5) using a 3D-printed adapter (pictures of the lock and adapter below), since this is a battery free solution while still negating the need for carrying a key. It works well and simpler might actually be better, but fingerprint sensors are just a bit cooler.

Temporary manual solution