As 7002T said, you can pull out then down on the area to the right of the LED on the unit. TC49A’s only chirp when they are first powered up, or when the cover is replaced. And if you’re replacing it, I’d be interested in it.
I unfortunately did not win the Sears SA120 rebrand, I bid 4 times and was outbid instantly on all 4 tries, and the price went up to $57 which is ridiculously expensive, even for a rare smoke detetctor.