Some bike lock manufacturers provide their own internal security ratings for guidance. That might help, but the most secure locks we’ve tested use standard ratings from objective sources, including Sold Safelywhich offers ratings for many vehicle types between Bronze and Diamond, and ARTwhich uses a numerical scale from 1 to 5.

So what do these ratings really mean? Here’s a guide to two of the top lock-security companies and their rating systems:

Sold Safely established in 1992 by Northumbria and Essex police in the UK. The brand is now owned and operated by the Master Locksmiths Association, a not-for-profit trade group. It uses a four-level rating system, as listed below.

Sold Secure Rating Levels: Bronze (lowest, safe against basic tools); Silver (midrange, safe against improved tools / determined attacks); Gold (second best, resistant against dedicated tools/attacks); Diamond (highest, resistant to damaging attacks and “special tools”).

The company also used separate ratings for different types of vehicles, such as bicycles versus motorcycles (now called pedal cycles and powered cycles, respectively). For example, Hiplok DX has Sold Secure Pedal Cycle Diamond rating and a Sold Secure Intensified Cycle Gold rating. It’s a good score, but it’s not as secure as top grinder-resistant options like the Litelok X1 or harder locks like the Litelock X3 and Hiplock D1000, all three of which earned Diamond ratings in both categories. Grinder-resistant locks are often mentioned directly on the brand’s site as well. When in doubt, you can always go to Sold Secure website to check if your lock is rated.

ART is a Dutch independent security firm that uses a five-star security system centered on vehicle type, durability, weather, environmental resistance, and resistance to attacks.

ART Rating Levels: 1/5 (minimum security rating, suitable for second bicycle lock only); 2/5 (higher security rating representing good theft protection for bicycles, the minimum for most insurance companies); 3/5 (bicycle security for high risk of theft, also suitable for mopeds and scooters for insurance purposes); 4/5 (very high security rating for bicycles, good theft protection for motorcycles while traveling); 5/5 (highest security rating, sometimes required to insure motorcycles stored at home).