The System Sensor 2151 is a low-profile plug-in photoelectric smoke detector with a 2" (5.1 cm) profile. It pairs with the 400 Series adapter bases and runs on either 2-wire or 4-wire conventional fire alarm systems, depending on which base you choose.

The sensing chamber is sealed against back pressure, dirt, and insects, with a fine mesh screen that can be cleaned or replaced. Two LEDs blink in standby for 360° visibility. The custom IC inside cuts false alarms.

Why the 2151 still ships in volume after decades

The 2151 has been a default specification in commercial fire alarm systems since the 1990s. Two reasons it stays in service: the 2" footprint fits nearly any retrofit ceiling, and the adapter base ecosystem (B110LP through B401) means one detector head covers most wiring scenarios you'll encounter.

• 2" low-profile design
• Pairs with the 400 Series product line
• Two LEDs blink in standby for 360° visibility
• Custom IC cuts false alarms
• Tamper-resistant base with shorting spring
• Chamber sealed against back pressure, dirt, and insects
• Cleanable or replaceable mesh screen
• Hand-held sensitivity reader available (SENS-RDR)

Commercial and industrial applications

• Commercial buildings (offices, retail, hospitality)
• Industrial and manufacturing facilities
• High air-velocity zones up to 3,000 fpm
• Conventional 2-wire and 4-wire fire alarm systems

Compatible adapter bases: B110LP, B112LP, B114LP, B116LP, B401

• B110LP / B110RLP: 2-wire base, 12/24 VDC, 10-130 mA alarm current
• B112LP: 4-wire, 24 VDC, with current limit resistor and Form A&C contacts
• B114LP: 4-wire, 120 VAC, with Form A&C and Auxiliary contacts
• B116LP: 2-wire base with Form C relay contacts, 24 VDC
• B401: standard 6" flanged base, 12/24 VDC
• B401BH-2: sounder base (requires external 24 VDC)