Ian,
This is a bit vague in what you are looking for and needing.
Is there a certain sound you are looking for? Freq/dB rating?
What is the interval between and length of tone?
How are you looking to power this?
Are you thinking about an analog solution or a small micro to control the sound.
Is there a battery life consideration you are looking at? How long will this sound at timed intervals need to continue?