Whether on the street lamp or in the basement, usually only a good lock can help against bicycle thieves.
U-locks, folding locks and chain locks in particular promise security - but often wrongly, as a study by Stiftung Warentest shows.
The testers examined 20 locks - using methods that bicycle thieves use: They hit the locks with special tools, bolt cutters, pliers and battery-operated angle grinders.
Every fourth lock could be picked astonishingly quickly.
The Luma Carpenter folding lock and the Abus Tresor chain lock only withstood the attacks for a few seconds.
In addition, the locks were examined for handling, pollutants and durability - such as corrosion resistance.
These five locks achieved an overall rating of "good" in the test:
Abus Granit Xplus 540 / 160HB2 (U-lock, grade 1.6)
Abus Bordo Granit Xplus 6500/110 (folding lock, grade 1.9)
Decathlon B'Twin 940 (U-lock, grade 2.0)
Abus Citychain 1010/110 (chain lock, grade 2.0)
Kryptonite Kryptolok 990 (U-lock, grade 2.0)
According to the test results, good locks do not have to cost three-digit sums.
The price of the Decathlon B'Twin is 36 euros, the Kryptolok 990 is available for around 50 euros.
The most expensive model (Abus Bordo Granit Xplus 6500/110), on the other hand, costs a whopping 128 euros.
Those who rely exclusively on theft protection and place less value on the absence of harmful substances and convenient handling may find other suitable models.
In our picture gallery we have listed the locks which, according to Stiftung Warentest, are the hardest to crack and which achieve grades between 2.0 and a smooth 1.0 in this category:
The bottom line is that weight seems to protect against theft.
The eight particularly protective models weigh between 1.3 and 2.6 kilograms.
Ironically, the heaviest tested lock is an exception - the chain lock Dr.
Mabuse III from the manufacturer XLC.
The lock, named after a literary villain, weighs 2.9 kilograms - but scored poorly with a 4.2 rating for security against being broken.
In addition, it could no longer be opened after the corrosion test.