Smart postbox?

Hey guys,

I am a complete newbie to electronics stuff, so sorry if my questions are too obvious. However I did some googling and still didn’t find answers.

So, the idea I have is to receive a notification on my smartphone every time I receive a letter in my postbox. The postbox has a small door which is being lifted to push through the letter - see the picture attached. So I thought to use a light sensor that could detect the opening of the door due to the light entering. However I am not sure whether the sensor is able to detect such a quick change as it is in this use case (I guess 1-2 sec of light) and I am not sure which sensor to use:
photoresistor like this ( or the light sensor module (

Another approach could be probably to use the infrared proximity module but the postbox has a weird shape and its quite narrow at the bottom part where the letters are ending up…

Could you please share your ideas about the feasibility of such an idea and which sensor / approach you would recommend?


There have been several of these here - probably the biggest problem you are going to run into is how do you get the information from the sensor/controller inside the box to anywhere else? Most of those boxes are metal and therefore, you are not going to be able to get any kind of rf signal out of them (well, very high frequencies could escape while the little door is open, but that is it). See Faraday Cage for a better explanation.

Thanks a lot for a reply.

Indeed that's a second part of the question I didn't touch upon. And the box is metal, true. It is located relatively close to my apartment - so what you see on photo is the outer part where the postman places the letter and I have the access to the box from inside of the building.

so I made a small test today placing the phone into the box through the outer little door and it was receiving some wi-fi signal from my flat though the lil door was somewhat open. tmrw I'll place the phone to the closed postbox to see if it still catches the signal. But that's a samsung phone and I have no clue how good the ESP8266-03 (WI-fi module I have) receives a signal... You think its not gonna work? Maybe in worst case I can mount the ESP somewhere outside.

Any feedback to my initial question? You mentioned there were similar projects? Thanks a lot! Appreciate your help!

Yes, don't remember the title right off hand, but search the forum for "mailbox" or "postbox" (your side of the pond). If you put a small hole in the back where you have access with a rubber grommet for protection of the wire, then you could run the wires to a sensor outside of the box. The problem with the light sensor idea that comes to mind (especially in winter) is it may be dark when the postman puts things in so it would not see anything happening.

Thanks, I found one thread with a "postbox".

Nice input - with a winter stuff... Then maybe its smarter to use an IR receiver at the bottom and IR LED at the top - so that when the letter is there IR signal can't pass through, does it sound more feasible? I just have to see if I can physically locate this stuff in - since the lower part of the box where letters are lying is quite narrow. i was inclined to light sensor since I could locate at the entrance where i have more space. But lets see.

For the wires I should give it a try, but not sure how safe it is - I don't know if some bulleys gonna break my system down - it is still a multifamily house! :slight_smile:

Or may be even simpler than IR receiver and IR LED transmitter - simply IR motion detector: letter is falling, so the motion detected?