I have a perfectly functional but old Pixel 4a sitting in a drawer collecting dust. The screen is broken, and the frame has a slight bend in it, but it’s otherwise okay. For a long time, I thought I had found the perfect way to reuse my old Android, but there are even more ways you can put yours to use.
There are tons of sensors in your phone that can be used for all sorts of smart home applications, including a presence sensor. And as you can probably guess, your old phone is more than equipped to handle that.
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9 Ways to Make Your Old Android Phone Useful Again
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This isn’t your typical smart home setup
Replacing expensive sensors with something you already own
Unfortunately, you can just read raw sensor data from an old phone and plug it into your existing smart home implementation. That is, unless you’re running Home Assistant. It’s a free, open-source smart home hub that lets you consolidate all your existing smart devices, including any phones, into one clean dashboard that you can manage how you see fit.
You can run Home Assistant on anything from a Raspberry Pi to an old laptop you’ve got lying around. If you don’t have a machine to spare, you can also install it as a virtual machine or Docker container. Home Assistant also sells Home Assistant Green, a dedicated single-board computer that comes with all the software you need pre-installed for $199. Although the pricing may vary among individual retailers.
By installing the Home Assistant Companion app on your old Android or iPhone, you can tap into the various sensors on your phone and use them to trigger automations via Home Assistant. In this case, you’ll be turning your old phone into a BLE (Bluetooth Low Energy) beacon, which will pick up signals from your primary phone to detect whether you’re present in a room or not.
- OS
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Windows, macOS, Linux, Raspberry Pi
- Developer
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Open Home Foundation
- Price model
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Free, Open-source
A self-hosted, open-source smart home platform that lets you control, automate, and unify all your devices locally without relying on the cloud.
It’s easier to build than you think
A simple setup that gets you up and running fast
Once you’ve got your Home Assistant up and running, start by downloading the Home Assistant Companion app on both your old phone and your current daily driver. From this point, it’s a four-step process to get everything working.
First, you’re going to need to enable the BLE Transmitter sensor on your primary phone:
- Open the Home Assistant app, tap the hamburger menu icon in the top left, and then tap Settings.
- Scroll down and tap the Companion app option.
- Under Sensors, tap Manage sensors.
- Scroll down to find the BLE Transmitter sensor and tap it to open properties.
- Enable the Enable sensor slider to start BLE monitoring on your old phone.
Make sure to note the UUID shown for your device. This is going to come in handy later when we’re creating our automations. Then, you’ll have to enable the Beacon monitor sensor on your old phone:
- Open the Home Assistant app, tap the hamburger menu icon in the top left, and then tap Settings.
- Scroll down and tap the Companion app option.
- Under Sensors, tap Manage sensors.
- Scroll down to find the Beacon monitor sensor and tap it to open properties.
- Enable the Enable sensor slider to start BLE monitoring on your old phone.
Once active, your old phone will start scanning for nearby BLE iBeacon signals and report everything it detects. At this point, you should see your primary phone UUID if you scroll down the sensor page with a number. This means your old phone is detecting signals from the current one, and your presence sensor is essentially working.
- OS
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iOS, Android
- Price model
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Free & Open-Source
- App Type
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Smart Home Moitoring
- Open-Source?
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Yes
The Home Assistant Companion App is a mobile app for Android and iOS that connects your phone to your Home Assistant server, enabling remote control, notifications, and sensor-based automations.
Now there are several ways you can use this reading in Home Assistant to create presence-based automations. I ended up creating a template binary sensor, which I use to trigger automations.
Screenshot by Yadyullah Abidi | No attribution required.
To do that, head over to your Home Assistant server settings and find the Helpers section under Devices & integrations. Use a template to create a binary sensor that checks whether your primary phone’s UUID is present as a non-null attribute in the old phone’s beacon monitor.
You will need the sensor name of your old device for this. For my Pixel 4a, it was sensor.pixel_4a_beacon_monitor. Yours will likely be the same, except you’ll need to swap out pixel_4a with whatever you named your phone when installing the Home Assistant app. The logical condition you need is this:
{{ state_attr(‘sensor.device_name_beacon_monitor’, ‘your_UUID//’) != None }}
Screenshot by Yadullah Abidi | No attribution required.
When the attribute exists, meaning the device is in the room, the binary sensor turns on. When it disappears, it automatically turns back off. Once the binary sensor is in place, automation becomes trivial, and you can use the sensor as a trigger to control anything connected to your Home Assistant hub. And that’s it, your old phone is now a presence sensor.
Mounting it is the real challenge
Power, placement, and making it look clean
Yadullah Abidi / MakeUseOf
Wall mounting your phone might be challenging, depending on what your walls are made of and how exactly you want to mount your phone. Mine currently sits in a bookshelf, but I’m working on a 3D printed case that allows me to keep the phone plugged in while displaying the screen in landscape so I can see the Home Assistant dashboard on the screen as well.
A phone permanently plugged into the wall will also take some damage to battery life, which is something you should keep in mind if you’re considering using the phone for other purposes as well. You can use the battery status sensors to automatically enable or disable charging based on your phone’s battery percentage, too.
Turning an old phone into a reliable presence sensor
That old phone sitting in your drawer is packed with sensors that you can use to pull off some extremely useful (and cool) automations in Home Assistant. All it takes is a few minutes of tinkering to get the app installed and sensors enabled, and you’re good to go.
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I replaced my smart speaker with an old Android phone and it does so much more
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You will have to keep the old phone plugged in permanently and perhaps mount it somewhere sensible, but all of that is much more useful than spending on yet another smart home device, which can be a pain to set up. There are things your old Android phone does better than any dedicated gadget, meaning that seemingly useless old phone can be a surprisingly capable part of your smart home setup, without needing to spend a single dime.