Magnetic Interlock

Magnetic interlocks form part of the Warp Drive system aboard starships, as part of the Warp Core assembly. Magnetic interlocks can be disrupted by subspace vacuoles. (VOY: "Emanations")

The exact function of the magnetic Interlocks is unclear, however it is generally believed that they are in some way responsible for the maintenance of a uniform magnetic field or bottle that is present inside the Dilithium Crystal Chamber. This field is critical to contain and direct the massive energies created by the annhilation of matter and Antimatter that power the Warp Drives on federation starships.

There seem to be two interlocks one on the port side and one on the Starbaord side. It is generally believed that because of the forces that they are constantly dealing with that they require two devices to maintain a strong enough magnetic field to remain effective. there is no indication that these are located anywhere but as part of the Warp Core ASssembly.

During the battle with the Duras sisters in 2371, the starboard interlock of the USS Enterprise-D took damage, and required reinforcement. Subsequently, the interlocks ruptured, leading to a Plasma Coolant leak, and eventually a warp core breach that destroyed the secondary hull. (Star Trek Generations)

Following sabotage by the True Way to the USS Orinco, the magnetic interlocks on the runabout failed, leading to a warp core breach. (DS9: "Our Man Bashir")