When I used a car-top carrier I purposefully would leave the door opener inside the house to make myself get out of the car and open the garage door. As far as insurance, look into an Inland Marine policy to cover your bikes.

From BustedCarbon.com:

"Yet another victim of the roof carrier system and garage combination and an absent-minded father.

The conversation went as follows:

Father: How was your day?
Son: Pretty rubbish actually.
Father: It’s about to get worse...
Son: Where is my bike??"