I cobbled the following together from bits and pieces I found on mailing lists. Seems straightforward, but the code I've included just sits there. The awaitSignal seems to be causing a problem, in that if I remove it (and don't call forever recursively) then I get my ALARM 5 sec later. Otherwise nothing. The problem is that if I don't include awaitSignal, then, of course, forever is called just as fast as the CPU will go :-) Brian import System.Posix.Signals import System.IO import Control.Concurrent alarm = do putStrLn "ALARM" hFlush stdout return () forever = do putStrLn "foo" scheduleAlarm 5 awaitSignal Nothing yield forever main = do installHandler realTimeAlarm (Catch alarm) Nothing forever