The 36-year-old, who had been without a club since leaving Bournemouth at the end of last season, has agreed a contract until January.
Flahavan has been signed after Newcastle United recalled Freddie Woodman from his loan spell.
"We wanted a keeper with lots of experience and Darryl certainly fits the bill," manager Mark Yates told Crawley's website.
Flahavan previously spent almost eight years with Southend and has also been at Crystal Palace, Oldham, Leeds and Portsmouth.
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Crawley Town have signed goalkeeper Darryl Flahavan on a short-term deal.