Do you need these dead locks for insurance ?
My advice would be not to bother and don't leave anything of value in the car.
Train station car-parks have cameras, so do most public/council buildings.
You can also fit cameras at home these days for not a lot of money if you are that concerned.
You havent said where you are - is it a really dodgy area ?
Full of theives and druggies and have-nots ?