From the car manual:
"Radio equipment on a similar frequency canaffect the key. If this happens, move the key atleast one foot (30 cm) away from otherelectronic devices (phone, laptop, etc). If thekey does not work, you may need to changeits battery. If the key’s battery is discharged,you can open Model S by following theunlocking procedure (see Unlocking When theKey Doesn't Work on page 7)."