Most stolen bikes are simply lifted away in silence. 110 decibels changes that.

How does an alarmed disc lock work?

1. 1Locking the wheelA hardened pin passes through the brake disc and locks. The wheel can only turn a centimetre or two before the lock fouls the caliper, so the bike cannot be wheeled away.
2. 2The alarmAn accelerometer distinguishes wind and passing traffic from lifting or rolling. Genuine movement triggers a siren loud enough to be heard across a street and to make a thief abandon a job that depends on silence.
3. 3Why noise matters mostBike theft is usually a two-person lift lasting under a minute. Noise removes the one thing that makes it work, which is why an alarmed lock outperforms a heavier silent one in the street.
4. 4Use the reminder cableAlways run the bright reminder cable to the handlebar. Riding off with a disc lock fitted is the classic self-inflicted damage, and the cable is what prevents it.

Disc locks and grip locks, compared

The alarm is the variable, not the steel. Sensitivity, battery life and whether the body physically fits between your disc and caliper are what separate these in practice.

What it does not do

Most pages about this product only tell you the good part. These are the objections raised by owners and locksmiths, and they are fair ones.

What changes once you own it

Where this fits

On a bike the two risks arrive together — being hit because nobody saw you, and losing it while it is parked.

The collision records show how much of the harm in each area happens in darkness, and how much of that happens where there is no street lighting at all. That second figure is the one that decides whether reflective material is enough on its own. Theft is the other half of the same trip: most riders lose more nights to worrying about where the bike is parked than to the ride itself.

1. 1

   Why does being seen after dark come down to more than dark clothing?

   Retroreflective material returns light to its source, so a driver's headlights pick it up at roughly three times the distance of dark fabric — at 30mph that is most of the stopping distance. It is the cheapest intervention available and the one with the largest effect per pound.

   But reflection needs a light already aimed at you. On an unlit road, or approaching a junction from the side, there may not be one — which is what the dark-and-unlit share for your area is telling you.

   Bike cover with lock loops →

2. 2

   It is parked. What rating do I actually need?

   The grade your insurer specifies, in the category that matches your vehicle. Sold Secure attack-tests within categories, and the thresholds differ — a motorcycle Gold is a harder test than a bicycle Gold. Reading only the colour on the box is how people end up under-locked and, at claim time, outside their policy terms.

   And a rating is a time, not a guarantee. What the bike is locked to matters as much as the lock, and the lock should never rest on the ground.

   Sold Secure bike lock →

3. 3

   What stops it being wheeled away while I am not there?

   A disc lock immobilises the wheel, and the alarmed version adds noise at the moment of interference — which matters because most opportunist theft depends on nobody looking. The rule every rider learns the hard way is that the reminder cable is not optional: riding off with a disc lock fitted is how forks get bent.

   You are reading this step

See the whole sequence on one page · Visibility advice is usually a slogan rather than an explanation, and lock ratings are quoted without anyone explaining that a Gold for bicycles and a Gold for motorcycles are different tests.