It's hard to find a family in america that has never lost a bicycle to a thief, especially these days since there's a tool that can cut through any lock in a matter of seconds. Well, tonight, we have... See More
It's hard to find a family in america that has never lost a bicycle to a thief, especially these days since there's a tool that can cut through any lock in a matter of seconds. Well, tonight, we have new evidence that bike owners are fighting back. And abc's sharon alps fyn alfonsi takes us along with ingenious citizens to test this. This is a bicycle that cost 2 grand. Reporter: When jake saw his stolen bike on online, he decided to consult the seller. This is seattle. Reporter: In tow, cameras rolling. You're under citizen's arrest. Stop now. Stop! Reporter: Police moved in and made the arrest. I think it's a lesson for thieves they need to be afraid of people like me. Reporter: Others have chased down thieves, too. Watch these office workers tackle these guys. They got the bieblg back. But police warn being a vigilante is a bad idea. Locking up your bike, a better one. We got to a legendary bike mechanic in new york city. Have you a helmet on your head, a messenger bag, they're well-dressed. Reporter: And they have a secret weapon. This is an expensive, top-rated steel bike lock. Done. Reporter: Oh, my gosh, that takes two seconds. Exactly. Reporter: Professional thieves swap bikes so they can easily sell them. Bill says there are things you can do to protect yourself from an amateur thief. Make sure the pole is securely in the ground. If they can lift the pole off they'll take the bike home. If the wheel drops off, the front wheel drops off. It's very difficult to take off the wheel. Reporter: And nothing is foolproof. Watch this. Unable to break the lock of this bike, attached to a tree, these guys just chop the tree down. Sharyn alfonsi, abc news, new york.
This transcript has been automatically generated and may not be 100% accurate.