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Gaciron Loop-100 Smart Brake Bike Tail light



Good little gadget for the money, picking up most braking motions reliably
Two mounting options
Battery indicator
Doesn't pick up very gradual braking motions
Rubber band mount feels a little flimsy

At every product is thoroughly tested for as long as it takes to get a proper insight into how well it works. Our reviewers are experienced cyclists that we trust to be objective. While we strive to ensure that opinions expressed are backed up by facts, reviews are by their nature an informed opinion, not a definitive verdict. We don't intentionally try to break anything (except locks) but we do try to look for weak points in any design. The overall score is not just an average of the other scores: it reflects both a product's function and value – with value determined by how a product compares with items of similar spec, quality, and price.

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As its name suggests, the Gaciron Loop-100 Smart Brake Tail Light is a rear light and brake light in one, using a motion sensor to register when you apply your brakes, which then triggers the brake light. It works well with most kinds of braking, although isn't sensitive enough to pick up very gentle motions. In addition to the braking sensor it has six modes, and a handy battery indicator gives you a rough idea how much juice it has left in the tank.

For more options – with and without braking sensors – check out our guide to the best rear bike lights.

> Buy now: Gaciron Loop-100 Smart Brake Tail Light for £17.49 from Gaciron

As a rear light, the Loop-100 works well. It has six modes, three of which emit a steady light at differing levels of brightness, with the other three being flashing modes. Trail mode is a quick bright flash, Power Saving is a low slow flash, while Fog Light is somewhere between the two.

While the 'brake' light is 100 lumens, Gaciron doesn't list the strength of the other modes, but they're bright enough to keep you visible in varying weather conditions.

The mode you put the light on doesn't affect the brake light either – it works in any of the six settings. It's also brighter than of those, so it's always obvious that you're braking. Well, it is if it's working...

Braking performance

When you're braking at a rate that the sensor can detect, the brake light will always be triggered. It was consistent at detecting all emergency braking, and the kind of braking motions you use to turn off at a junction, or stop at a traffic light. It never once faltered on these.

What it did not pick up, however, were subtler movements – like when applying the brakes very gently while crawling through traffic, or when travelling at just a few miles per hour and slowing over a long distance. The movement just wasn't strong enough to trigger the brake light.

To give you an idea of what this looks like in numbers, I paced out 30m. At the beginning of the 30m I'd hit the brakes, with enough force to slow down my bike at a consistent pace over the 30m distance. I'd then hit the start of the 30m at different speeds, with the following results:

  • Going from 20mph to 0mph over 30m – brake light activates
  • Going from 10mph to 0mph over 30m – brake light activates
  • Going from 5mph to 0mph over 30m – no brake light

It wasn't the 5mph speed that was stopping the brake light from getting triggered, it was the distance over which I was gradually slowing. When I did an emergency stop from 5mph, you can see from the video that the light does trigger. It would appear then that the brake light comes on for most braking motions, but not quite all. It's not like a car brake light in that regard.

That said, when I'd slow to start climbing a hill, the brake light (quite rightly) wouldn't flick on. If it was able to pick up the subtler braking motions I tested it on, then I imagine it would also flick on when your bike slows to go uphill, which wouldn't be ideal either.

Battery & run-times

The Loop-100 charges via USB-C and takes 2.5 hours, with the on/off switch turning blue to indicate it's fully charged.

2023 Gaciron Smart Brake Bike Tail light LOOP-100 - USB port.jpg

When turning the light on, the on/off button will display as blue for a few seconds if there's more than 60% left in the tank. This changes to yellow for 20-60%, with a red flash for less than 20%.

When it gets really low, the light will start switching itself off every 30 seconds or so. I found that a bit annoying, since it has the battery indicator anyway – I don't need to know that it's running out by having to constantly reach round while riding and turn it back on.

Battery life varies between 5.5 and 40 hours, depending on which mode the is in. This will also vary depending on the amount you brake.

In the brightest mode, it's supposed to last approximately 5.5 hours. To remove the variable of the brake light, I took it off my bike and kept the light turned on. And yes, since it cuts out every two minutes, I did spend over 5 hours of my life either walking around or shaking it every time it cut out to bring it back to life. It started turning itself off completely at around 5 hours and 10 minutes.

One of my favourite features was how the light automatically shuts off after two minutes, when no movement is detected. As soon as movement is detected, it automatically switches itself back on. As someone who often forgets to turn their bike lights off, only to return later in the day to find they're flat, this got a big thumbs up from me.


The Loop-100 comes with two mounting options: a tool-free option that attaches to the seatpost, and a bracket that fits under the saddle.

2023 Gaciron Smart Brake Bike Tail light LOOP-100 - side.jpg

With the seatpost mount, a piece of rubber sits between the mount and the seatpost to keep it from slipping. A rubber band then clips onto each side of the mount, wrapping around the post. It stayed in place on my rides, but I'm not too crazy about the longevity of mounts like this – I've found they eventually snap, though who knows, I might be proved wrong here. The second one that mounts under the saddle is a little fiddly to fit at first, but screws on nice and tightly.

2023 Gaciron Smart Brake Bike Tail light LOOP-100 - mount.jpg

During testing I switched between the two and found the light always stayed put, helped by the back of the light being magnetic to correspond with a magnetic strip on each mount.

2023 Gaciron Smart Brake Bike Tail light LOOP-100 - back.jpg

It's also quick and easy to take the light off the bike. You just press down on the release button and glide it off. Easy peasy.


It's also worth mentioning that the Loop-100 has an IPX6 waterproof rating, which means it'll keep working in any wet conditions as long as its not completely submerged under water. I rode in a couple of rain showers and it lived to tell the tale, helped by the USB-C charging port cover fitting snuggly.


At the time of writing, the Loop-100 is listed on Gaciron's website with an rrp of £22.64, the seemingly randomness of its price due to the exchange rate, though it's actually discounted to £17.49. That's pretty good value compared with many of its competitors.

We haven't tested it, but the G-Keni Smart Brake Light, for example, has a similar spec – it uses a motion sensor to detect braking, has two mounting options and will automatically cut out when no movement is detected – but costs £29.99.

The Sigma Blaze Rear Light is £27.99 and has longer run-times than the Loop-100, but no flashing mode, and the waterproof rating is slightly lower at IPX4. Iwein also thought the mount was a little flimsy.

The BBB SignalBrake Auto Brake that we reviewed last year has a slightly better spec, with an IPX7 waterproof rating and a faster charge time of 1hr 45mins, plus a "watch strap" style mount rather than a wraparound rubber band, but it's £36.99.


The Loop-100 is a good little gadget for around £20. While it didn't pick up very subtle braking motions, it lived up to all its other claims and worked reliably. If you're in the market for a bike brake light, it does a solid job for the price.


Good little gadget for the money, picking up most braking motions reliably test report

Make and model: Gaciron Loop-100 Smart Brake Bike Tail light

Size tested: 100 Lumens

Tell us what the light is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?

The Gaciron Loop-100 Smart Brake Light is both a rear light and a brake light, using a sensor to detect braking motion. It does this pretty reliably, although the brake light doesn't get trigger if you're slowly crawling through traffic.

Tell us some more about the technical aspects of the light?

Gaciron lists the spec as the following:

Charging: USB-C

Light Source: COB

Material: Aluminium Housing

Max Brightness: 100Lumens

Working Modes: 7

Visible Beam Distance: >1000m

Dimensions: 33.5*30.2mm

Net Weight: 25g

Charging Time: Approx 2.5 hours

Max Runtime: 40 Hours

The seven "working modes" includes the brake light mode. The modes all worked as expected, with the charge and run time living up to the spec.

Rate the light for quality of construction:

It's early days, but the light casing looks to be well made and pretty durable.

Rate the light for design and ease of use. How simple was the light to use?

It's quick to turn on and off – you're not having to hold the on/off button for a few seconds as you do with some lights.

Rate the light for the design and usability of the clamping system/s

It comes with two mounts. The mount that attaches to the saddle bracket screws on and stays put. The mount that attaches to the seatpost uses a rubber band which feels a little flimsy, though it hasn't failed (yet). It's easy to glide on and off each of the mounts. You just press the release button and slide it off.

Rate the light for waterproofing. How did it stand up to the elements?

It has an IPX6 rating, and kept working in downpours.

Rate the light for battery life. How long did it last? How long did it take to recharge?

It takes about 2.5 hours to recharge, with its battery life lasting between 5.25 hours and 40 hours.

Rate the light for performance:

Fine as a rear light, and consistently detected most braking motions, though struggled to pick up that I was braking if I was crawling through traffic.

Rate the light for durability:
Rate the light for weight:
Rate the light for value:

Tell us how the light performed overall when used for its designed purpose

It matched up to all the claims, just not picking up on subtler motions.

Tell us what you particularly liked about the light

The automatic cut-out. If no motion is detected after two minutes, it will turn itself off, turning back on when you're on the move again.

Tell us what you particularly disliked about the light

The seatpost mount. The rubber band seems a little flimsy and I'm not convinced it will last particularly well – though I might be proved wrong!

How does the price compare to that of similar products in the market, including ones recently tested on

It's well priced at just over £20. There are a few brake lights out there that are £10-£16 more, but then they have better mounts, waterproofing and recharge times.

Did you enjoy using the light? Yes

Would you consider buying the light? Yes, if I was in the market for a brake light.

Would you recommend the light to a friend? If they were wanting a brake light, then yes I would – I think it does fine for the price.

Use this box to explain your overall score

It's a good little gadget for the money, working well as both a rear light and a brake light, aside from more subtle braking times.

Overall rating: 7/10

About the tester

Age: 27  Height: 5ft 4  Weight: 147lbs

I usually ride: Dawes Galaxy  My best bike is:

I've been riding for: Under 5 years  I ride: Most days  I would class myself as: Experienced

I regularly do the following types of riding: commuting, touring, general fitness riding,

Add new comment


TobyinHelsinki | 7 months ago
1 like

I've got one of these except I bought it from Alpkit where they are badged up as Alpkit Halos. 19.99 full price but I bought mine on a discount for 15. I've been really pleased with mine so far. The only problem with them is the temptation to look between your legs, not ahead, when braking to admire the braking light function!

bigwheeler88 | 7 months ago

Nice idea, but doesn't seem to do much based on the video. And a light getting brighter will do nothing to the drivers that at best aren't looking and at worst are looking but don't care.

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