An erstwhile colleague of mine worked on the component that destroyed the Ariane 5; it performed exactly to spec, detecting that the vehicle was out of control - due to the integer overflow (in another, unrelated component nb) - and self-destructing it to prevent it crashing to earth. However explaining this subtlety to a rabid press was a different story, and the whole thing became a bit of a PR disaster
Nothing too fancy, just strategically placed explosive charges to break up the vehicle to stop it from traveling further down range and disperse the propellant to reduce the size of the explosion.
I think you misunderstood - the purpose was to self-destruct the rocket, so although I don't know the details I'd imagine it was a sensor to detect the vehicle exceeding its flight parameters coupled to either an explosive packet or something in the fuel system to make the rocket go bang
