Almost every current smartphone can read NFC tags. These tags are available as round discs that can be attached inconspicuously and can withstand wind and weather. If you have the Home Assistant app installed on your smartphone, you can use it to write to and read tags. you can get 40 NFC tags for less than 13 euros and it’s worth buying a larger quantity, because once you’ve started using them, you can think of countless possible applications.
One of my applications is controlling my cistern pump and an irrigation valve. I can supply a tap with water from the cistern. You can find details about my DIY irrigation controller in this article:
DIY irrigation control with Home Assistant and ESPHome
Unfortunately, there are practically no wireless switches based on ZigBee, Bluetooth or WLAN that are suitable for outdoor use. However, I always have my smartphone with me anyway and, together with the NFC tag, I can easily switch the pump and valve with it. I also have protection against unauthorised use - it only works with my smartphone.
The new NFC tag is described once with the HA app and is then displayed in Home Assistant under Settings -> NFC tags. You can now create an automation based on the desired tag. The trigger is When a tag is scanned -> Names of the tag
In my case, the “Water tap” automation should first check whether the fill level of the cistern is above 15 % (instructions for a DIY fill level meter can be found HERE ) and if so, trigger my irrigation controller to switch the pump and the corresponding valve.
Now all I have to do is hold the smartphone over the tap for a moment to control the pump.
There’s a tag hidden under my desk that I can use to control the socket for the power supply to my desk or one on the outside of the garage that controls the garage door.
The best way to attach the NFC tags is to roughen one side with sandpaper beforehand so that the adhesive holds better. Indoors, an all-purpose adhesive , double-sided adhesive tape (the one from 3M is bombproof ) etc. will do. On plaster and stone, hot glue or mounting adhesive holds well and reliably. You can also plaster the tags in if it is not deeper than 10 mm or hide them behind wallpaper and thin wood - just try it out first.