Try disconnecting the battery in the smoke detector and if you have a carbon monoxide detector, disconnect the battery there too. As a previous poster stated, high pitched chirps are deceiving as to their source. Look in ALL your drawers in EVERY room in the area to see if something like a pager isn't on a low battery. One time I put my pager in a desk drawer off of the kitchen. It took my wife and I about 20 minutes to find it. And that was only after we started rummaging through the drawers!
If all else fails, you can shut the main power off to the house and see what happens. If it stops, you know you can start looking for something plugged in. Do you have any electronic devices like a wall phone, a portable phone, or an emergency spot light that has battery backup in it? If so, maybe something like that is chirping. Look for a cellular phone or a pager or that smoke detector. Take the batteries out of EVERYTHING until you find out what it is. WHEN YOU DO, LET US KNOW!