Fearing someone as he fears Allaah or greater is shirk, is looking inside cars near your house because you think the enemy is inside one of them waiting to attack you shirk. The reason he looks inside these cars is to make sure nobody is there so he can safely leave the house and if someone is there he waits inside his house until that person in the car leaves.
Wa’alaykum as Salam wa rahmatullahi wa barakatuhu,
No, this will not constitute Shirk.
It is permissible to take caution, and ensure you are safe.
And Allaah Ta’aala knows best
Ismail Moosa (Mufti)