The Immobilizer was an experimental piece of technology invented by the Decepticons as a secret weapon. It fired a blue beam of energy that froze a Transformer's servos in place, rendering them incapable of movement, leaving them frozen and immobile. It was destroyed by Knock Out, who used it to knock Starscream unconscious in Predacons Rising. According to Bumblebee, it causes instant Stasis-lock, though the victim remains fully conscious, a living death.
Arrival to Earth
The Decepticons stationed on Earth later discovered its location. Airachnid and Starscream were sent to retrieve it. Airachnid later betrayed Starscream and left him in the middle of no where. Airachnid took the Immobilizer and fought the Autobots. Bumblebee then manages to trick the Decpticon and the Autobots recovered the weapon. 
Battle Over the Omega Lock
Bulkhead equipped himself with the Immobilizer and froze many Vehicons during the battle on Cybertron. After Megatron reveals that he has kidnapped the kids and threaten to expose them to Cybertron's atmosphere, Bulkhead had to surrender the Immobilizer to the Decepticons.
Eventually, the Immobilizer was found in the wreckage of the Omega Lock. Like all relics, it was placed in the vault of the Nemesis. When he went to find the Star Saber, Smokescreen walked past it.
Bumblebee used a Predacon bone (called it the Immobilizer) to show Predaking as he and the Autobots found him at the burial site. Bumblebee explained that they didn't come to fight him, but to find answers of the existence of two Predacons. Despite turning against Megatron, Predaking didn't follow the Autobots but he did return to help them defeat Unicrom with Skylynx amd Darksteel. Sometime later, Starscream used the real Immobilizer against Bumblebee. Bumblebee tricked him by saying it wasn't the real device. Though after a short battle over it, Knock Out used the Phase Shifter to get the Immobilizer from Starscream and hit him with the device, destroying it in the process.
- Bumblebee (tried getting it from Starscream )
- Knock Out (Destroyer)
- The Immobilizer is a callback to the Wheeljack Instant Immobilizer from the The Transformers episode "The Immobilizer".
- A similar object that could immobilize things appeared in Transformers: Animated.