18 wild uses for your old Android smartphone

Your old smartphone can be used as an ideal gym device. Reformat the device to remove unnecessary apps, take out the SIM card, and don’t log into Facebook or Twitter via WiFi, and you’ll avoid any unnecessary notifications that could interrupt your workout.

Then take your pick of the countless fitness-tracking apps out there and boot it up — or just pack it full of music and use it as an MP3 player when out and about or on the treadmill.

Bonus: Pair it with a cheap fitness tracker or smartwatch for extra functionality.

Apart from its physical form, a smartphone is indistinguishable to a normal computer — so why not treat it as such? Even the oldest smartphones out there are considerably more powerful than desktop computers were even 20 years ago.

Explaining every step of the process would take more space than available here, but here’s a link to a tutorial on how to install Debian — a version of the open-source Linux operating system — on your device. Then just connect it to a monitor, sync up a bluetooth keyboard and mouse, and you’re good to go.

Load up your smartphone with mapping apps (think CityMapper, Google Maps, Waze, and anything else that takes your fancy), mount it on your dash, and voila — you’ve got a dedicated GPS unit that won’t interrupt your journey with phone calls or notifications. With an aux cable, it can even double-up as a dedicated stereo/MP3 player for your car. Who needs a Tom-Tom?

If you're going hiking, you can also use the device as GPS-powered map to help you stay on track. There are plenty of offline-compatible apps around that let you download the maps in advance — so you can navigate areas without signal, so turn off your mobile connection manually to save battery.

Google Cardboard is one of Google's coolest projects — with a $20 (£13) kit (or some cardboard and a sharp knife), anyone can build a DIY virtual reality headset.

Some of the apps available are still pretty-rough-and-ready, but if you want a low-cost VR headset to show off to your friends, this is currently your best bet.

There are also a number of more expensive Android-compatible VR kits if you feel like splashing out — or don't want to have to build it yourself.

Just be aware: Cardboard requires your smartphone to have a gyrometer to function properly, and cheaper phones (both old and new) often don't include one.

Who uses an analogue clock these days? Take your pick of the thousands of clock apps in the Google Play Store, buy yourself a cheap smartphone dock, and you’ve got an infinitely customisable alarm clock to sit beside your bed.

You can even use your old smartphone as a portable charging station for your current device.

With a cheap USB OTG (On-The-Go) cable, you can connect two smartphones together. The "host" phone will then automatically start charging the other one with its battery.

Pick up a USB OTG cable, and keep your old smartphone switched off and charged in your bag, and your new device will never run out of battery while out and about again.

Buy yourself a Chromecast streaming device (or a micro USB-to-HDMI cable), reformat your old phone, and fill it with apps like Netflix, Hulu, YouTube, Spotify, and Pandora. You've now got a dedicated TV topbox with a remote/living room media centre.

If you're plagued by weak Wi-Fi, you can boost the signal throughout your house by installing an app like fqrouter2, which will pick up the signal and repeat it. It will require rooting the device to work; here's a tutorial on how to install the app.

Sure, turning your device into a desktop computer is cool, but do you really need it? Rainforest Connection puts old smartphones to a more noble purpose — protecting rainforests from deforestation.

Donate your device to the organisation, and it will "erase it, retrofit it and send it into the jungle for its second life as a tireless forest guardian," listening out for illegal logging.

Take advantage of your device's camera by turning it into a Wi-Fi enabled security camera to protect your home. Apps exist that are motion-sensitive and will email the owner with photos; here's a tutorial on how to set it up.

To turn your smartphone into a digital photo frame, just install an app like Dayframe, load up a selection of your favourite photos, sit it in an upright dock, and let it roll.

So, we’ve established that Android smartphones are computers. You know what else is technically a computer? A robot. And yes, with a bit of work you can turn your Android smartphone into a functional robot brain.

There are multiple examples of smartphones being used to power robots. Take the Cubestormer 3, which can solve a Rubik’s Cube in 3.253 seconds and is built out of Lego. Or the Smartbot, which is programmable and can navigate, hear and “see." Or you can build one yourself, using around $30-worth (£20-worth) of kit.

Apps like Dormi and the simply-named Baby Monitor transform an old smartphone into a baby monitor, streaming video and audio to your current device.

It's well-known that children love touchscreens. But having to hand over your shiny Samsung S6 to a dribbling toddler isn't ideal. So take your old device, set up a Restricted Profile to limit their access, and install a set of kid-suitable apps like "Angry Birds." Children entertained, worry free.

For those occasions when it's all gone wrong: Wipe the phone, put in a pre-paid SIM card, and store it in your car or at the bottom of your bag — preferably with an extra charging pack or battery just in case. That way, if you've ever in trouble, you know it's there for you to rely on.

As long as your device still works fine, you can use it to help contribute to modern scientific research via its processing power. Folding@Home is probably the best-known such app, using a devices unused processing power to try and find cures for cancer, Ebola, Alzheimer's and more.

BOINC is another option, released by the Space Sciences Library at Berkeley, that lets users choose from a variety of projects including space research and global warming modelling.

Another selfless option for your obsolete smartphone: charities like Oxfam will take your smartphone and either repurpose it, send it overseas or recycle the parts for cash to fund their operations.