Whether it’s building storage servers from outdated PCs, turning refurbished thin clients into retro emulation machines, or reusing dinosaur laptops as FOSS-hosting workstations, I’m a huge fan of recycling old hardware. While most of my DIY projects involve devices belonging to the PC, smartphones and tablets are fair game, too. Considering that typical phones pack a lot of sensors, they can double as makeshift smart devices. In fact, I’ve paired some ancient phones with my Home Assistant stack, and they worked so well that I ended up using them to replace a handful of conventional smart gadgets.

I use my phone-powered Home Assistant satellite all the time

It’s even more effective with an AI-powered voice assistant pipeline

If you’re a Home Assistant aficionado, you’ve probably spotted the assistants section hidden deep within its web UI. But unless you’ve got dedicated hardware, getting the assistant to work with all the entities in HACS can be a pain – even more so when you want to build a voice-controlled setup that uses a wake word before listening for input. You’d either have to grab the proprietary Voice Preview system or look into a DIY setup involving microcontrollers/single-board computers, microphone modules, and a lot of programming wizardry.

Or, you could take the easy path as I did by turning an old smartphone into a Home Assistant satellite. Thanks to a recent update to the Home Assistant Companion app, smartphones can listen for wake words and process voice commands locally. By default, my old phone can only detect certain trigger words to pull up the Assist section, but the real fun begins when I add self-hosted LLMs to the mix.

For reference, I’ve got an old PC running an Ollama LXC, which I’ve paired with the Home Assistant to access my Qwen3 (8B) model as the conversation agent. I’ve also added Whisper as the speech-to-text server, while Piper is responsible for the text-to-speech conversion. Combine that with the wake word-detection capabilities on my smartphone, and I’ve got a full-fledged voice satellite for my Home Assistant server.

I’ve also built a dash cam with an old phone

But it can double as a local security camera, too

Besides the microphone, it’s possible to reuse an old smartphone’s built-in camera for DIY projects. For example, I use it as a dash cam for my car, which uses both the camera and a SIM card. The IP Webcam app lets me pull camera footage from my phone via RTSP streams, effectively turning it into a surveillance camera that I can pair with any ol’ Network Video Recorder tool. In my setup, that’s a Frigate server running on a mini-PC.

If I connect my smartphone to the same network as my Frigate system, this setup works really well as a local security camera for my house. But unlike typical surveillance cameras, modern smartphones support SIM cards, allowing me to use cellular networks instead of relying solely on my home LAN. In other words, I can use this makeshift security camera as a dash cam to transfer videos to my Frigate server even when I’m far from my home lab.

I could technically use port-forwarding to pair Frigate with my phone, but I rely on Tailscale instead, as my LAN is cursed with CGNAT. Since IP Webcam updates the IPv4 address of my smartphone when I connect it to my tailnet, I’ve had zero issues with this setup so far. I’ve also paired my Frigate setup with Home Assistant, so I can not only use it to trigger notifications when things go wrong with my dash cam, but also observe its stream directly on my HASS dashboards.

My phones also double as decent Home Assistant dashboards

I use the Bubble Card integration to design mobile-sized UIs

While we’re on the subject of dashboards, any smartphone with a functioning screen can display dynamic information, widgets, and buttons from Home Assistant. That’s because Home Assistant lets you create multiple dashboards, each with their own UI elements, and it’s possible to modify their size and appearance to better suit small screens – like the ones on typical phones.

In fact, I’ve built a couple of dashboards specifically for my smartphones via the Bubble Card integration from the Home Assistant Community Store. Bubble Card lets me condense all the sensors and buttons for controlling a gizmo under a single UI element, with each entity hidden inside a pop-up interface. That way, I don’t have a bunch of entities belonging to the same device on the UI, and I can even group multiple devices under the same module, making the overall interface a lot cleaner for my phone-based dashboard.

Don’t toss your old smartphone into the trash just yet

Besides the DIY projects I’ve mentioned so far, there’s a lot you can do with an outdated phone. I currently use an ESP32 as a Bluetooth proxy for my Home Assistant, but you can do the same with most smartphones. If you’ve got a 3D printer, you can create a wall mount for your phone and use it as a control hub for your smart devices (though I recommend using a large tablet for this particular project). Heck, you can put your dinosaur phone’s accelerometer to good use as a presence detection module for Home Assistant automations.