A lock-on is a technique used by peaceful protesters to make it difficult to remove them from their place of protest. It often involves handcuffs, chains, padlocks or bicycle locks. More complicated lock-ons involve protesters putting their limbs through pipes containing concrete, or a mixture of steel and concrete and is only limited by the imagination and ingenuity of those making the "lock-on". The willing protester can choose between a type that will allow them to willingly remove themselves or a type that requires machinery to remove them.

The safe removal of the protesters necessitates the involvement of skilled technicians, and is often time-consuming.

The lock-on chosen by the protester may be the difference between being arrested or not, or may vary the kind or number of charges brought against them by the police. If a protester can remove themselves when asked to by the police, they may stand a better chance of not being arrested. However, if they can remove themselves and they chose not to, they may receive a charge for refusing to remove themselves from the lock-on. If the protester cannot remove themselves, it is likely that potential charges are not as important to them as what they are protesting about.

"Locking on" is a very successful means of slowing down operations which are in truth or are perceived by the protesters to be illegal or immoral; it is also often used to allow time for journalists to arrive and record the scene and take statements from the group spokespeople.