Hi @Brikpilot, welcome!
Systems such as Tile are based on BLE (Bluetooth Low Energy) and use signal-strength measurements to determine proximity. Many people use this same method for presence detection in home automation, using either a BLE tag or a mobile phone as the target and tracking the signal strength from fixed position receivers.
This can be done using a Raspberry Pi, for example.
There used to be a system called Happy Bubbles that was an Open Source system to do exactly that. I have it set up in my house, but I haven’t used it much. Unfortunately the company behind that system is based in the US, and they had to close up because Trump’s import tariffs killed their business. All their designs and code are still online though if you want to dig into it:
Home Assistant has support for a BLE-based location tracking system, but I’m not a Home Assistant user so I don’t really know anything about it.
What I’ve written above might sound like it’s off-topic if you just wanted something simple to attach to your keys, and then find them using an app. However, the critical point is integration. The important thing to understand is that the magic little tags you attach to things aren’t magic, and they’re not unique to a specific supplier. They’re just a simple Bluetooth beacon.
My advice is to start by looking at the integration side, and work towards the tags, not the other way around. Look at what home automation system you’re running and what BLE support it has, then what you need as receivers to provide it the data, then what tags you should get to work with your receivers.
This is a really interesting topic that I’m planning to do a video about, but it’s some time down the track. Too many other topics to cover first