Cat Safeguard uses state of the art artificial intelligence to identify items that enter its detection zones--it can distinguish between animals, humans, and inanimate objects that might be blowing or rolling around under your vehicle.
When Cat Safeguard detects a presence under your vehicle it enters a threat detection and mitigation state that quickly evaluates the threat and engages (aka "sets off") a piercing alarm under the vehicle that appears to be simultaneously coming from everywhere and nowhere. The intent is that most thieves will get the message and won't want to stick around long enough to try and remove your converter--they'll go somewhere else where the pickings are easier.
If the thief runs off Cat Safeguard will continue to listen quietly in case he decides to return. Once Cat Safeguard decides that the threat is over it will resume its normal under-vehicle monitoring.
However, in the unlikely event that the thief doesn't get the message CAT SAFEGUARD will activate--that is, "set off" your vehicle alarm--including blowing your horn, flashing your lights etc., depending of course on your vehicle's alarm features.