Here’s a cool piece! A still sealed Universal from 1976! The picture on the box looks like a BRK 79DCRI!
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The Universal SmokeSignal SS-200 was a rebrand/variant of the BRK SS-218. I saw two at a house for sale years ago.
It came years before the 79DRCI, uses a 12.6v mercury battery. They succeeded the SS-74 which was the basic model and used a 10.7v battery. These are extremely rare, none are known to exist (the house these two were in was sadly remodeled and the detectors are long gone).