What does it mean when I try to start my cadillac and it doesn't start, and the screen on the dashboard reds "no fobs detected.

that means that the key fob is not reading to your car. you would have to check the battery in the fob if not then you have to go and reset the fob back to the car if you go batteries plus or the Cadillac dealership they can give you the instructions to reset the key fob. if that doesn't work then you have to buy another key fob. just had it done to my car last week to where I had to get key fob sinked back to my car and it was $90 to fix.

does the key fob unlock the door?