The Gentex 9123 has been discontinued.  Recommended is the Gentex S1209.  See feature comparison below.

A Gentex photoelectric, digital technology smoke alarm which can be tandem interconnected with all Gentex tandem capable smoke alarms, CO, alarms or combination smoke/CO alarms including 9123 series, 7139CS series, CO1209 Series and GN-503 Series. Utilizing DUALINK, if one interconnected S1209 alarm annunciates, then up to 12, interconnected units will sound their smoke and/or CO alarm warnings.

S1209 Features:

• DUALINK tandem interconnection capability of up to twelve smoke alarms
• 90dB (decibel), T3 (temporal) audible alarm
• 9V battery back-up
• Wall or ceiling mount
• Push button Self Test verifies power operation and battery levels.
• Functionality test button analyzes photoelectric sensing chamber for proper operation.
• Pulsing LED sensing chamber and condition indicator
• Mounting hardware adapts to standard junction boxes
• Quick-disconnect wiring harness
• UL Listed (USA)
• One year warranty

9123 Features:

• 90dB solid state non-latching piezo T3 audible horn
• Functional test switch - patented three position test
• Pulsing LED sensing chamber
• Solid-state LED condition indicator
• Tandem connection of up to twelve units
• Maintenance indicator
• Quick-disconnect wiring harness
• Mounting hardware adapts to standard junction boxes
• Wall or ceiling mount
• UL Listed (USA)
• 1-year warranty