Read section 3 of your manual. Or, I guess you could just keep rocking it.
Key Suspend Function
If a key is left in the vehicle, the functions
of the key left in the vehicle are
temporarily suspended to prevent theft of
the vehicle.
The following are inoperable:
l Starting the engine using the push
button start.
l (With the advanced keyless function)
Operating the request switches.
To restore these functions, perform any
one of the following:
l Press a button on the key which has
had its functions temporarily
suspended.
l For vehicles with a type A meter,
messages are displayed in the
instrument cluster.
(Manual transaxle)
When carrying another key, depress the
clutch pedal until the KEY indicator
light (green) illuminates.
(Automatic transaxle)
When carrying another key, depress the
brake pedal until the KEY indicator
light (green) illuminates.
Refer to Warning/Indicator Lights on
page 4-15.
Before Driving
Keys
Plus, a lot of these systems use more power from the key fob when it is in constant communication with the car so your fob battery may be low. When the car senses the fob it is constantly sending a signal back and forth as opposed to when the key is away from the car it is likely in a lower power mode.