Technically it doesn't break physics as its gravity wave that is detected, which is a ripple in space itself rather than matter / energy moving through space.
Assuming we go with that... your detector kicks off and detects a ship emerging from jump space at 100 AU. What are ya gonna do about it?? It's a week to send a ship to the point it arrived at, by which time the ship could be anywhere, even jumped back out.
For starters, it may have detected a misjump and might need some help.
If the ship jumps out, it creates another signature in the same time frame so you wouldn't need to continue moving assets to that location.
It needs to be thought of like radar, it allows you to know where to direct assets and reduce the number of patrols to provide the same coverage. ( Also can detect number of vessels that have jumped which is a major boost to readiness.)