The US Postal Service delivers mail, etc., to your mailbox every week from Monday through Saturday. Amazon packages may be delivered to your mailbox on Sundays. That means up to seven days a week, you may be receiving mail and/or packages to your mailbox. In some cases, mail delivery is incredibly consistent, so you always know when it should arrive. However, in a lot of cases, delivery time varies. You could check multiple times per day, or only check late in the evening, or, instead, you could set up a way to notify you when something has been delivered to your mailbox!

This guide will show you how to use the Feather ESP32 V2, CircuitPython, WiFi, and Adafruit IO to build a notifier that tells you when your mailbox has been opened. Once everything is set up, and the Feather is installed in your mailbox, you'll receive an email each time the door is opened!

This project requires that your mailbox be within range of a WiFi hotspot to which you have access, such as those found in your home. In the event that WiFi is not available, you should consider other radio options beyond the WiFi discussed in this guide.

Parts List

The following is required to build this project.

The Feather ESP32 V2 with the antenna connector will let you connect from further away.

Angled shot of rectangular microcontroller.
One of our star Feathers is the Adafruit HUZZAH32 ESP32 Feather - with the fabulous ESP32 WROOM module on there, it makes quick work...
Out of Stock

A reed switch detect when the mailbox door has been opened so the Feather can notify you.

A normally closed-capable magnetic reed switch. Reed switches are available as normally closed (NC), normally open (NO), or both. Normally closed is required for this project. The guide build uses a switch that does both, but only the NC connection is used.

Here is an example available on Amazon. Magnetic reed switches are available from many sources, so feel free to order from wherever you prefer. Simply make sure you check the specs before purchasing to ensure you are getting a NC-capable switch.

A battery is required, the larger the better. The following battery is ideal, but if it's unavailable, you can downsize to 6600mAh or 4400mAh if needed.

Angled shot of blue rectangular lithium polymer battery with 2-pin JST connector.
Lithium-ion (also known as 'liion' or 'li-ion') batteries are thin, light, and powerful. The output ranges from 4.2V when completely charged to 3.7V. This battery...
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An antenna is also required. Here are three options to fit various needs.

Angled shot of red rectangular antenna with wFL connector.
That's one slim cellular antenna! At about 220mm long from tip to tip and with a cable thickness of just 0.8mm, this 2.4GHz WiFi or BLE antenna is slim, compact, and...
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If you would prefer a larger antenna, you can purchase the adapter, and one of the antennae shown below. You do not need both antennae.

Angled shot of RP-SMA to IPEX3 antenna adapter.
Most antennas have SMA or RP-SMA connectors on them, how are you going to connect them to your little RF module? This little cable will bridge the two!This adapter cable is...
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Short 2.4GHz Dipole Swivel Antenna
This 4"/100mm long swivel dipole antenna has 2dBi of gain and 50Ω impedance so it will work fantastically with just about any 2.4-2.5GHz wireless receiver/transmitter such...
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Long 2.4GHz Dipole Swivel Antenna
This 8"/200mm long swivel dipole antenna has 5dBi of gain and 50Ω impedance so it will work fantastically with just about any 2.4-2.5GHz wireless receiver/transmitter such...
In Stock

Optional but Highly Suggested

To make it easier to remove the hardware from the mailbox, this project uses Command Small Picture Hanging Strips, which are adhesive hook and loop fasteners used to mount things.

If permanent adhesive is used, it will make swapping or charging the battery, and updating CircuitPython on the Feather, much more difficult. Therefore, some way to remove things more easily is suggested. These strips are one option.


For measuring the current draw of the project, for example during deep sleep, a Nordic PPK2 is a lifesaver. This project has taken low power into account, but if you wish to verify your own build or another design, this is the instrument to have.

Angled shot of Nordic nrF Power Profiler board.
The Power Profiler Kit II is a standalone unit, which can measure and optionally supply currents all the way from sub-uA and as high as 1A on all Nordic DKs, in...
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This guide was first published on Sep 14, 2022. It was last updated on Apr 13, 2024.

This page (Overview) was last updated on Mar 08, 2024.

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