The 7103 was discontinued a few years back.
The S1209 is 120V but has a 9V battery backup.
The S1209 has a different wire harness and mounting bracket than the 7103 if you replace the existing 7103s.
Lastly, the tandem feature. The Tandem feature is if one smoke trips ALL the smokes trip that are tandem together. If there are 7103s still at the Hospital and they add the S1209s these 2 units DO NOT tandem. If that is an issue, they will need to replace all the smoke detectors. They cannot mix together. The S1209 can tandem up to 12 units.
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