How can I utilise my old Android device?

Absolutely, there are many ways you can repurpose an old Android device. Here are a few ideas:
Digital Clock or Alarm Clock: Install a clock app that can display the time in large digits, and you've got yourself a new digital clock. You could even use it as an alarm clock.
Media Controller: If you have a home theater system or a smart TV, you can use the old phone as a dedicated media controller.
E-Book Reader: Install an app like Kindle or Google Play Books and turn your old phone into a dedicated e-book reader.
Security Camera: Apps like Alfred can turn your phone into a security camera. You can place it in a strategic place in your home and watch the live feed from your primary device.
Digital Photo Frame: Load it up with your favorite photos and use it as a digital photo frame.
Dedicated Game Device: There are plenty of games that can run on older devices. You can turn your old phone into a dedicated gaming device.
Fitness Tracker: Install an app that can count steps, measure distance, etc., and use it as a dedicated fitness tracker.
Remote for Smart Home Devices: If you have smart home devices, you could use the old phone as a dedicated control device.
Offline GPS: You can use it as an offline GPS for your car. Apps like Google Maps allow you to download maps for offline use.
Learning Tool for Kids: If you have young children, you could load it up with educational apps and games and give it to them.
Just be aware that the device might not be as fast or responsive as when it was new, and you might have to deal with limited battery life. However, for many of these purposes (like a digital photo frame, e-book reader, or digital clock), you could leave the device plugged in.
- I was gonna say nice ai generated response but then i noticed hour username.
- I like the security cam idea.
  
  I just used the Alfred app when I left my house and it works great even accessing from an iphone. Lots of features are pretty much free like recording and speaking/listening through the camera, there's just a bunch of ads and you can only view it through one device simultaneously.

Here's a few! :)
Making it a dedicated E-reader
Portable entertainment device (movies/TV etc)
a pc stats monitor (screen for CPU temps etc)
emulation device
digital photo frame gallery
if you also have a really old phone laying around (talking the ones before touchscreens with the number pad) they would make a great mp3 player
It's generally recommended that you put a lighter weight OS onto the phone. Many are available depending on what you want to do and work much better on older devices than android (which updates tend to get heavy and demand more power which unfortunately slows old devices).
I'm planning to do this for a couple old devices and then repurpose them with other uses
- Any particular lightweight OS recommendations? I'm thinking of doing something similar with an old tablet I have
  
  I'm still looking myself, but Corvus OS is recommended for performance and gaming. There are a lot out there and depending on what you want to use it for some will be more suited. Here's a link I found a while back that lists a few good ones :) https://techviral.net/best-custom-rom-for-rooted-android/
- Any recommendations for using it as a PC stats monitor? That could be an interesting one for mounting near the PC!
  I think the displays may be too small for use as a photo frame or e-reader though (love the Kobo for this).
  
  A lot of people seem to use apps, one called 'Remote System Monitor' looks good, and then connect a charging cable to the pc to keep it charged.
  Personally I'd love if there is a way to do this not involving phone apps, but instead reducing the old phones capabilities to just a screen and having the pc recognise and use it as one. That could lead to some interesting possibilities.

Welcome! Will keep this up since there are already some great responses below, but for the future I'd just flag rule 2 and that we ask questions be posted to !askandroid@lemdro.id. Thanks!

LineageOS.. turn it into a hardware air gaped crypto wallet, a tv remote control, a web cam, a security cam, a second device to play games with friends visiting, gift it to the local shelter, make it your second backup of your password manager, development board for Android apps, etc

I use old android as webcam with DroidCam.

My last phone become the streaming remote for a year before I finally sold it.

The re-usability of a phone is almost nonexistent thanks to the battery, that is a fire hazard. You leave it plugged in as a surveillance camera? Your home burns.
If you can actually remove the battery and power it on without one. Just then is everything back on the table.
If you can't? Recycle please.
- You don't really know how Li-on batteries work, do you?

I use my old android as a dedicated lemmy reader while laying awake before sleeping/alarm clock that never leaves the bedside table.

If you want to find other examples, there was a subreddit for this specific purpose called androidafterlife. Not aware of a Lemmy equivalent

We have a Moto G7 Power which we turned into an e-reader for my wife. She was constantly chewing through her primary phone battery doing this so I offloaded it to the Moto which has been great. With the 5000mah battery (I know, that's standard these days), and it's primary responsibility of displaying text on screen, ti's made a good stand in.
As other's have said, Android webcam, there are plenty of apps out there, I use "IP Webcam" by Pavel Khlebovich from the Play store which is no cost and does the job quick and dirty.
If you are into home automation, some people have placed old phones near windows and taken advantage of the light sensors built in (Which regulate the auto screen brightness), and used those to trigger indoor lighting events based on the light level where if it's darker inside, then lights on or gradually turn lights on accordingly. . Or, use the proximity sensor used to turn screen of when near your ear and create a trigger if something came close to it, IDK what you'd want to monitor being close by, but let your imagination fly! Home Assistant is great for this, their companion app, reveals soooooo many sensors on the Android device which can it can act upon. It's crazy.
Donate the phone to a non profit charity. This is a good list of places: https://www.androidauthority.com/where-to-donate-old-cell-phones-3311699/
Use older apps on the old phone which aren't compatible with newer Android OS api's. For example, Prior to them yanking the app, I used an old Samsung phone to use Rockstar's Ifruit appa as it wasn't compatible with newer Android phones, to take care of my dog in GTA V.

I use my old Galaxy S9+ to run all my smarthome apps. There's so many janky apps for various smarthome devices that I don't want on my personal phone. I created an entirely seperate google account for the phone and have all the awful apps running on it. The goal is to have it also power a display with a Home Assistant dashboard. I also have it on a separate vlan so if it gets hacked/compromised they can't access the other computers on the network.

I use mine to broadcast to BT speakers when I'm out in the woods, on the water, whatever. No use draining my main phone just to listen to tunes.

If you've got a 3d printer, an old phone is often a great octoprint host. It's got a built-in camera and everything.

Cold wallet for crypto.
- People still have crypto?
  
  Very, very cold wallets 🥶.
  
  I hope so.

Smart home remote control?
It'll make a good remote display of any kind too.
Do try to see what custom ROM you can load it on, I'm pretty sure you'll need to run a fairly recent version of Android for it to be moderately useful.

Get one of those telescoping type-C game controllers and turn it into a poor man's Logitech G Cloud. Those controllers usually have a battery in them, to top up the weak battery in the old phone. Use it on Wifi for Xbox Streaming or Moonlight, or put a SIM card in it for Xbox Game Pass or Geforce Now on the go.
- Got a recommendation for something that has a battery? I think the Gamesir one is nice but I'd like one that can charge the phone like you're suggesting!

Another use you can give it is an offline, turn by turn navigation gps. OsmAnd is an excellent app that provides you with offline navigation. Install something else, like a modded Youtube Music/Spotify app or even AntennaPod if you're into podcasts and you pretty much have a cheap, budget Android Auto unit. Sure, it will not be the best of all, but it's pretty much free at that point, and it will get the job done.

I love this idea actually I've been wanting an e-reader besides my phone

I'm actually using an old Android I had laying around and collecting dust (Huawei P20 Lite), battery was pretty much flopping, but as a Linux user tried to give it a second life and made a sort-of Android TV box of it.
I installed a TV launcher and 2 main apps (SmartTubeNext and Cloudstream), then connected it to my main Linux laptop through cable and run a program called scrcpy which let's me duplicate the image/audio to a separate window in my laptop. Cheap and dirty, but it works flawlessly.