Energy efficient passive entry system

1. A passive entry system for a vehicle comprising:

a vehicle-based communication system mounted in a vehicle; and

a portable communication device;

wherein said vehicle-based communication system includes a transmitter for transmitting a challenge signal to said portable communication device when in a polling state to determine a presence of said portable communication device for allowing access to said vehicle;

wherein said portable communication device includes a receiver for receiving said challenge signal, and wherein said portable communication device is responsive to said challenge signal when in a response state and non-responsive to said challenge signal when in a non-response state, said portable communication device being placed into said non-response state in response to receiving a lock-out signal from said vehicle based communication system.

2. The passive entry system of claim 1 wherein said portable communication device continuously receives said challenge signal from said vehicle based communication module while in said non-response state.

3. The passive entry system of claim 2 wherein said non-response state includes a power down state for terminating power to said receiver and transmitter.

4. The passive entry system of claim 3 wherein said vehicle-based communication system determines whether said portable communication device is within an interior of said vehicle for an extended period of time and transmits a power down signal for placing said portable communication device into a power down state.

5. The passive entry system of claim 4 wherein said portable communication device is powered up after a first predetermined period of time.

6. The passive entry system of claim 4 wherein said portable communication device is powered up on a manual button actuation of said portable communication device.

7. The passive entry system of claim 1 wherein said vehicle-based communication system determines whether said portable communication device is within an interior of said vehicle and transmits said lockout signal for placing said portable communication device into said non-response state.

8. The passive entry system of claim 7 wherein said vehicle based communication module transmits an exit signal to said portable communication device for exiting said non-response state.

9. The passive entry system of claim 8 wherein said exit signal is transmitted in response to said vehicle based communication module determining said portable communication device is exterior to said vehicle.

10. The passive entry system of claim 8 wherein said exit signal is transmitted in response to said vehicle-based communication system receiving an unlock request signal from a respective keyless entry device.

11. The passive entry system of claim 8 wherein said exit signal is transmitted after a predetermined period of time.

12. A method for conserving power in a portable communication device of a vehicular passive entry system, the method comprising the steps of:

broadcasting a challenge signal from a vehicle base communication module to said portable communication device;

broadcasting a response signal in response to said challenge signal;

determining if said portable communication device is within an interior region of said vehicle; and

broadcasting a lockout signal for placing said portable communication device into a non-response state it said portable communication device is within said interior of said vehicle.

13. The method of claim 12 wherein said portable communication device only receives challenge signals when in said non-response state.

14. The method of claim 13 further comprising the step of transmitting an exit signal to said portable communication device for determining said location of said portable communication device.

15. The method of claim 14 wherein said exit signal is transmitted in response to at least one predetermined condition occurring.

16. The method of claim 12 wherein said portable communication device neither receives challenge signals nor transmits response signals when in said non-response state.

17. The method of claim 16 wherein said predetermined condition is selected from the group comprising elapse of an extended period of time, activation of a vehicle function, and actuation of said portable communication device function.

18. The method of claim 12 further comprising the step of determining whether said portable communication device is within an interior region of said vehicle for an extended period of time and transmitting a power down signal for placing said portable communication device into a power down state wherein power to said receiver is terminated while in said power down state.

19. The method of claim 18 further comprising a step of powering up said portable communication device after a first predetermined period of time.

20. The method of claim 18 further comprising the step of powering up said portable communication device in response to a manual button activation of said portable communication device button.