Why would both key less entry remotes simultaneously stop working?

Be sure your car battery is good before anything.If your car battery is good try to reprogram the remotes. To Program Wireless Remote Transmitters: Begin with: S The driver's door open and unlocked. S Key out of the ignition. 1. Insert and remove the key from the ignition switch 2 times within 5 seconds. NOTE: Steps 2 and 3 should be performed within 40 seconds. 2. Close and open driver's door TWICE. 3. Insert the key into the ignition and remove it. NOTE: Steps 4 -- 6 should be performed within 40 seconds. 4. Close and open the driver's door twice. 5. Insert the key into the ignition. 6. Close the door. NOTE: Steps 5 and 6 should be reversed for the following models ONLY (close door first, then insert key into ignition): S 2000 -- 2005 Celica S 2001 -- 2003 Prius S 2001 -- 2005 ECHO S 2001 -- 2005 RAV4 S 2003 -- 2004 Avalon 7. Turn the ignition switch from “Lock” to “On” and back to “Lock” at about 1 second intervals to select the desired mode: S 1 time for ADD mode. S 2 times for REWRITE mode. S 3 times for CONFIRMATION mode. S 5 times for PROHIBITION mode. 8. Remove the key from the ignition. 9. To confirm your mode selection, the power locks will now cycle “lock” to “unlock” a number of times corresponding to your key cycles in step 7. NOTE: If Confirmation or Prohibition modes have been selected, opening the door will complete the procedure.