Problem with setting timer

I've been programming a RFID security system (using Serial) for my motorbike and Im getting stuck programming codes for this action: when turn on the power, in 5s if there're no tags be put close to the reader, the siren will be turned on. Basicly, if in 5s an action is not done, another action will be done. Any help will be appreciated, thank you :).

You error is in line #37. That's my best guess since you didn't post your code.