Immobilizer

A powerful experimental weapon, the Immobilizer can be used to freeze Autobots in their tracks.

Prime cartoon
The Immobilizer was being transported on board the Harbinger when the ship was shot down over Earth by an Autobot battalion. The portion of the ship containing the Immobilizer came to rest against a cliff face, and there it remained until Airachnid located it (not without Starscream's help) and extracted the weapon from the wreck. She then lay in wait with it, using the Immobilizer to freeze first Bulkhead and then Optimus Prime, intending to present them to Megatron as trophies. The third member of the Autobot team, Bumblebee created a dust cloud with his blasters, which Airachnid fired the Immobilizer into. When it cleared, Bumblebee stood frozen, but he was merely feigning and used the opportunity to sneak up on Airachnid. After punching her, he shot the Immobilizer, shattering it. The Autobots later retrieved the pieces and Ratchet repaired it so he could unfreeze Optimus and Bulkhead.

The Immobilizer was among the many weapons Jack showed to newcomer Smokescreen on his tour of the Autobot base Bulkhead took it out of storage to use when the Autobots were returning to Cybertron to try to get the Omega Keys back. It worked really well on the Vehicons, and the Autobots were able to recapture the Keys. With the kids hostage to the Decepticons, Bulkhead threw down the Immobilizer.

The Immobilizer was stored on the Nemesis. The Autobots intended to use it in battle against Unicron, however Starscream got hold of it first and attempted to retake the ship with it. He didn't reckon on Knock Out turning against him, snatching the weapon from him and belting him with it. Unfortunately the Immobilizer was broken as a result.