Which one is it?
Look at what the car itself does. If the interior lights come on, the dash lights up and the horn works, the car's battery is alive and the fob is the likely problem. If the car shows nothing at all, no lights, no chime and no screen, the car's battery is the problem.
A message on the dash saying the key isn't detected means the car is awake and can't hear the fob.
Starting a car with a dead fob
Cars are built to start even when the fob's battery is dead. Most fobs have a passive chip that the car can read when it is held very close. Where you hold it depends on the car: against the start button, against a marked spot on the steering column, or in a slot or tray in the console. Then press the brake and press the button as usual.
Your owner's manual shows the spot, usually in a section about a weak fob battery.
Some cars are fussy about position. If the car still can't find the key, try again with the fob pressed right on the spot, and keep your foot firmly on the brake until the car responds.
Getting in when the fob is dead
Most fobs hide a small metal key. A little release button or latch slides it out. On many cars the keyhole on the driver's door is hidden under a cap on the handle, and you can pry the cap off with the key.
Opening a door with the metal key can set off the alarm on some cars. It usually quiets down once the car recognizes the fob or you start the engine.
Replacing the fob battery
Most fobs take a small coin cell, often a CR2032, though some use other sizes. Open the fob (the manual shows how), note which way the old cell faces, and drop in the new one. It takes a couple of minutes.
Fob batteries usually warn you first: the range shrinks, the buttons don't respond every time, and you have to stand right at the car before it notices you. Read the number on the old cell before you shop, because coin cells that look alike differ in size and thickness.
When it is the car's battery
If the car's battery is the one that is dead, a new fob battery won't help, and the remote may not unlock the doors either. Use the metal key for the door, then get the car jumped. A car battery that is close to dead can behave strangely first, with a start button that needs several presses or a dash that restarts itself, and that is easy to mistake for a fob problem. A jump start is $49–$75, plus the $19 dispatch fee, charged once.
If you can't get into the car at all, because the metal key is missing or the lock won't turn, tell dispatch. We also do vehicle lockouts, and the driver confirms you own the car before unlocking it.
Common questions
The range shrinks, buttons stop responding every time, and the car sometimes doesn't see the key until you stand right next to it. Many cars also show a low key battery message.
No. The fob and the car have separate batteries. A jump start only helps when the car's battery is the one that is drained.
No. They are separate. A fob can go dead on a car whose own battery is perfectly healthy.