To silence the 755PSMA you need to press and hold the buttton on the front of the smoke detector for 10-15 seconds not only will it silence the alarm but it will also reset it.
Some of the key features are:
New look design with easy to use test/hush button
Easy installation and maintenance
Wired interconnect feature (up to 40 alarms)
Optional relay or wireless interconnect bases
Backwards compatible with 755PSMA and 755SMA mounting bases