I bought a £16 smartwatch just because it used USB-C

https://shkspr.mobi/blog/2025/08/i-bought-a-16-smartwatch-just-because-it-used-usb-c/

Look, I'm an idiot. I know that, you know that, and the man on the moon knows that. Let's not get into why I'm an idiot; let's just accept that I have my peculiarities and you have yours. My idiocy is a quest to make sure all my portable electronics can recharge using USB-C.

Modern smartwatches are tiny and they do a lot. As a consequence, their battery life is generally poor. The industry's attempts to fix this are either to replace the charging standard every year hoping to find something magical, or to lock you in to a walled-garden on proprietary nonsense.

I want to recharge my watch while I'm riding the bus. That means plugging one end of a USB-C cable into the seat and the other into my wrist. That's how I recharge my phone, eReader, laptop, headphones, toothbrush, and a hundred other gadgets. Why should a watch be any different?

So I bought the only smartwatch I could find with a USB-C port. The Colmi P80 - on offer at £16. It bills itself as "The world's first type-c smart watch".

To be clear, I wasn't expecting this to be a good smartwatch. Anything you buy from AliExpress for the cost of a couple of pints is bound to be a bit crap. What I wanted to know is whether USB-C charging of watches is viable.

What I discovered is that, yes, USB-C charging works even on a relatively small watch. Oh, and that this is a surprisingly decent bit of kit - especially given its price. Let's dive in!

Video Walkthrough

If you'd rather watch and listen than read a blog post, please enjoy this shonky video:

What Works?

It tells the time accurately!

You can set it up without using the app (more on that later). It Bluetooth paired to my phone without a problem - and without PIN entry. I could make and receive calls from the watch - and the voice quality was adequate.

Tilting the watch up made the display come on! I wasn't expecting that, to be honest.

The jog-dial button works. Good for scrolling and clicking.

Swiping on the screen to navigate works with pretty good accuracy.

Vibration notifications were strong enough to be noticeable.

There were a bunch of simple games and apps on there - including 2048 - which all ran fine.

The built in torch (!) was bright and useful.

And, yes, it charged via USB-C!

Charging Speed and Battery Life

It claims a 0-100 in 90 minutes which seemed broadly accurate.

It came with a short USB-C to C lead which was charge-only, no data. I plugged it until fully charged, then wore it continuously. After 24 hours of use, even with all my fiddling, that battery was at 80%.

After four days, it still had 40% left - I'd been using it for exercise, sleep tracking, a couple of phone calls, and using the torch at night. After 5 days, I finally got the "low battery" warning when I hit 20%. I reckon, with moderate usage, you'd squeeze a week out of it. Sticking the brightness up, keeping the screen on longer, and playing music through its tiny speaker are also going to drag the battery life down.

My USB-C Power Meter said it charged at 5V .16A, that's around 0.8W. Slow, but it only has a small 280mAh battery. Bluetooth Low Energy is, unsurprisingly, pretty energy efficient! Heart monitoring and motion detection is also a low-power activity. There's no power-guzzling GPS or cellular connection - so the power requirements are pretty modest.

The rubber flap keeps the port safe, although does feel a little flimsy. If you have a chunky cable, it might interfere with the cover a little.

Update after 2 weeks of use: Over about 9 days, the battery went from 100% to 20% - that was using it for a few exercise sessions, getting notifications, and continual heart-rate monitoring. Once the battery got bellow 20%, it wouldn't let me start new exercise monitoring or other activities. So you should easily be able to get a week of useful use out of this.

Power Delivery

This does not work with PD chargers. If you plug this in to the same power-brick as your laptop, it will not charge. Based on the three that I tried, PD chargers will not negotiate down to 1W levels.

If you have a charging adapter with multiple outputs, the regular USB-C ones will charge this just fine. All the USB-A to C chargers worked fine.

Heart Monitoring

Much like my friend Neil and his smartring from the same manufacturer, I've not benchmarked the accuracy of the heart-rate monitoring. When I exercise, it goes up. When I relax, it goes down.

It pegged my resting heart rate at about 65BPM, which in line with other devices. While walking on my treadmill, it went up to 100.

My SpO2 was measured as 99% which, again, was as expected. I held my breath for as long as possible and it dropped to 95%.

Within the app, you can set a "Heart Rate Warning" and various other detection settings.

Sleep Monitoring

I wore it at night. There's a "sleep mode" setting which stops the screen coming on, but you have to dive into a sub-menu to turn it on.

The watch showed this reasonably accurate screen:

The data are also sent to the app:

What's Annoying?

Given that this is a £16 watch, it hasn't exactly been "Designed by Apple in California". There are limitations and weird little niggles but, surprisingly, not too many.

First up, the brains of the watch is the JL7012 - which is a deliberately underpowered chip. It can do Bluetooth comms and drives the screen reasonably well. You're not going to be flinging billions of pixels around in 3D. The animation of all the interactions is a little jerky - obviously not 60FPS but just slow enough to be slightly annoying.

You can't tap the screen to turn it on; you have to click the side button or rotate your wrist. The raise to wake works, but takes a second or two to register. Weirdly, the scroll wheel works in most UI elements, but it doesn't for changing dates and times - so it is a bit of a slog to manually scroll through them on screen.

There no online manual available. All the other Colmi products have a manual available. Similarly, there's no firmware updates listed - although the app does claim to be able to update the firmware.

The USB-C port is for charging only - you can't get data off it via cable. You cannot use the watch while charging - once plugged in it will show a few messages about keeping the device clean. If you set it to use "nightstand" mode, plugging in will show the time and battery level - but you can't interact with any of the functions.

Directions - no maps, GPS, or even a basic compass. You cannot add any apps to this - what you get is what you get.

Connectivity - Bluetooth only. No WiFi and no cellular. This can't make emergency calls unless you're connected to Bluetooth.

Multiple alarms can be set - but you can't choose their ringtone.

You can add some "favourites" to the main screen, swipe across to get them. Sadly the options are pretty limited. For example, you can't put alarms or the calculator there. For those, you've got to dive into the main menu.

The screen brightness is manually controlled - no clever adaptive technology here. It can go bright enough to see in the blazing sunshine, although the dimmest setting is still a bit bright for night use.

There's no NFC - so you can't use this to pay for things. You can't even use it as an NFC business card - although you can send it QR codes to display, which is a handy alternative.

All that might sound bad but please remember that this is a sub £20 watch; it isn't competing with something costing ten times as much. The fact that it does all these things at all is pretty impressive!

Some of the functionality isn't available unless you pair it with the supplied app.

App

It is a given that all hardware apps are fundamentally a bit rubbish. The Colmi Fit app is basically fine. It isn't very polished but does everything it needs to do. You can get away without using the app completely for most things.

If you want updated weather, stocks, or prayer times - you'll need it to be paired to the app. Annoyingly, things like world clock also need a connection to be set up. Similarly, things like menstrual tracking need a connection (although, please note the privacy implications).

Annoyingly, despite it being basic Bluetooth functionality, music controls don't work without the app nor does the ability to show contact information.

Notifications other than calls also require the app. You'll need to give it permission to read all your notifications, but you can set it only to forward ones from specific apps. I didn't bother to set that up.

There are several built-in watch faces which can be changed by rolling the knob. Only one of the built-in faces is customisable:

What surprised me was just how many watch faces were available to download:

Sadly, I don't think it is possible to add your own designs, and none of them let you fiddle with what's displayed.

Many of the settings - like how long the screen should stay on for - are only available in the app. Even thought the app can get your location, you have to manually tell it what city you're in for an accurate weather forecast.

There were a few things I couldn't get working. The "AI Voice Assistant" is, I assume, just streaming audio back to your phone. As I don't have an assistant app, it didn't do anything. I'm not a Muslim, so I can't tell if the prayer times are accurate. The stress monitoring is a bit opaque - I don't know what precisely it measures. I don't have a menstrual cycle for it to track. I didn't investigate the SOS settings either:

Oh, and you can also tell it to remind you to drink water.

Finally, the app will show a notification showing your goals.

The app works well even if you deny it all the permissions it asks for but, obviously, some bits won't work unless they have access to your phone book, location, gallery, etc. You can always uninstall the app once done setting it up.

Exercise Mode

There are a bunch of different exercise modes on the watch - I'm not sporty enough to tell you what the difference is between all of them.

The app has some basic fitness stuff and will track your jogging locations.

Buried in the watch menu are your historic stats, but you'll need the app to export them.

Step detection is, like most watches, based on arm-swinging. So it wasn't terribly accurate when I was on my standing desk treadmill, but was acceptably accurate when going outside. It showed roughly the same amount of steps as the Pixel Watch 3.

You have to manually activate exercise mode if you want to quickly look up your heart-rate, steps, times, etc.

Instruction Manual

The leaflet in the box is the standard multi-lingual affair. Here's a quick scan of the English version. That'll show you some of what this watch is capable of.

Other Interesting Features

I got the cheapest strap possible - but it looks like it uses standard fittings if you want something more luxurious.

The 240x296 screen is bright and colourful - a basic screen protector is included in the box.

There's a built in LED which acts as a torch - which is only useful if you wear it on the left wrist.

The "Flappy Bird" clone is a bit crap, but 2048 and space invaders are reasonable time-wasters.

There's a camera shutter app if you want to use it as a remote control.

It claims to be IP67 waterproof, but warns not to immerse it in water or use it in steamy environments. It seemed to be splash resistant, but I didn't take it swimming or showering.

Security

There is none. There's no password lock on the screen and there's no Bluetooth PIN.

To be fair, there's nothing much you can do with the watch if you stole it. OK, you could make some phone calls if you were within range and get people's contact details. But there's no payment information stored. A thief might get your exercise and menstrual data, but it isn't a treasure trove of information.

Once it is paired to your device, it doesn't advertise itself via Bluetooth. If it is disconnected, it only broadcasts its availability when the screen is on. There's no pairing PIN.

OEM

The manufacturer appears to be Mo Young - they make the watch and the app.

They have some detail about the watch platform but not much.

Open Source and GadgetBridge

The device uses the MOYOUNG-V2 protocol. I was able to pair it with GadgetBridge by pretending it was a Colmi V79. Most of the functionality worked - I was able to see heart rate, steps, change some settings etc. I've requested GadgetBridge support which should make it possible to get notifications etc.

Update! GadgetBridge can now send notifications!The notifications can be read and deleted, they can't be replied to.

There are a few open source apps to create new watch faces and then upload watch faces to the device. But I wasn't able to get them working.

Disassembly

Update! There's a discussion on opening the device

smallsolar

@smallsolar@techhub.social

Like many people inspired by @Edent @blog I got a #colmiP80 but I'm not a watch person so for science I opened it up.

https://git.solarcene.community/smallsolar/Colmi_P80_Smart_Watch/src/branch/main/images

So - its not meant to be opened up, the back plate is glued in place, I heated it for a little while but then realised that its likely got a lipo sitting behind it so in the end just resorted to brute prying open. While initially I was able to partially open the lid any more and the small ribbon cables started to tear.

The good news is despite the heart beat sensor, the roller wheel and some other sensor now being fully detached the device does still turn on (sort of).

What I can see though are some interesting IC (well one) and also lots of nice test pads.

I can also see as predicted that the usb-c port is just 5v and GND.

In a bit I'll solder in the test points and see what I can find...

If you are interested there are some discussions on my IRC server (88.202.151.14 port 6668)

There are also some great photos of inside the watch.

What's Next?

My last smartwatch was the fairly crappy eInk Watchy which recharged with micro-USB, I only used it for a few weeks before getting bored of it. The last time I seriously tried to use a smart watch was a decade ago and I hated it.

Perhaps I'm just not a watch person? This is a cheap and useful way to get started. After a few days of use, I'm beginning to get used to it. It'll be more useful once I configure the notifications I get, I suspect.

Should I Buy One?

That's up to you, champ. I'm not your real dad and I'm not trying to take his place. But I'm here for you if you need me.

Anyway, as discussed in a previous post, this little device shows that it is possible to make a smartwatch that uses USB-C. It isn't the most powerful or customisable watch. It can't compete with a £200+ Apple or Android watch - but it is surprisingly capable.