There are many ways of detecting runway incursions. I have to say that dazzling the offending aircraft or vehicle with a l@ser is one of the more dramtic suggestions.
The problem has always been with integrating the detection system with existing procedures. Like so many systems the bugbear is too many false or nuisance alerts devaluing the system used.
In terms of an onboard system rather than an ATC based system I agree with OK465. Flight deck airport situation displays based on ADS-B don't just cover runway incursion but can help with taxiway navigation and taxiway conflict all in one system. No need for bells and klaxons - just an ability to see the whole picture regardless of airport conditions.