Simplex 4906-9128 — a ceiling-mount TrueAlert multi-candela audible/visible notification appliance combining a low-current electronic horn with a synchronized xenon strobe, in a red housing with white FIRE lettering, for SmartSync two-wire control.
The defining feature of this appliance is SmartSync operation. On a single two-wire notification appliance circuit, the horn and the strobe are controlled separately: the horn operates on-until-silenced while the strobe continues on-until-reset, so an operator can silence audible notification without dropping visible notification, and without running a second pair of wires. The horn can be driven with a Temporal pattern, March Time at 60 BPM, or steady, and every strobe on the circuit flashes at a synchronized 1 Hz rate so that multiple visible appliances and their reflections do not produce random flashing.
Strobe intensity is selected at installation by a selection plug at the back of the housing, with an attached flag in black lettering on a bright yellow background that shows the selected intensity beside the strobe lens. Because one model covers all four candela settings, site inventory stays small and mid-construction changes are easy to accommodate. The appliance installs to standard 4 in. electrical boxes, and the enclosure is both impact and vandal resistant.
Specifications
| Appliance type |
Ceiling-mount audible/visible (A/V), horn with multi-candela synchronized strobe, non-addressable |
| Housing color / lettering |
Red housing with white FIRE letters |
| Candela settings |
15, 30, 75, or 110 cd, field selectable |
| Housing dimensions with lens |
4 3/4 in. L x 6 7/8 in. W x 2 5/8 in. D (121 mm x 175 mm x 67 mm) |
| Rated voltage, UL |
Regulated 24 DC (16 VDC to 33 VDC absolute operating range per UL 1971) |
| Rated voltage, ULC |
20 VDC to 30 VDC per ULC S526-M878 |
| Maximum RMS current (nameplate rating) |
15 cd: 92 mA; 30 cd: 140 mA; 75 cd: 288 mA; 110 cd: 376 mA |
| Reference RMS current at 18 VDC |
15 cd: 76 mA; 30 cd: 117 mA; 75 cd: 222 mA; 110 cd: 284 mA |
| Reference RMS current at 24 VDC |
15 cd: 57 mA; 30 cd: 88 mA; 75 cd: 167 mA; 110 cd: 213 mA |
| Flash rate and NAC loading |
1 Hz, with up to 35 synchronized strobes maximum for each NAC |
| Horn output characteristics |
2,400 to 3,700 Hz sweep, modulated at a 120 Hz rate |
| Horn output at 24 VDC, 10 ft (3 m) |
UL 464 reverberant: 88 dBA steady, 84 dBA coded. Anechoic: 94 dBA steady, 95 dBA coded |
| Horn output at 16 VDC, 10 ft (3 m) |
UL 464 reverberant: 86 dBA steady, 82 dBA coded. Anechoic: 92 dBA steady, 91 dBA coded |
| Horn output at 33 VDC, 10 ft (3 m) |
UL 464 reverberant: 90 dBA steady, 86 dBA coded. Anechoic: 96 dBA steady, 96 dBA coded |
| Environmental |
32° to 122°F (0° to 50°C); 10% to 93% RH, non-condensing at 100°F (38°C) |
| Connections |
Terminal blocks for 18 AWG to 12 AWG (0.82 mm2 to 3.31 mm2), two wires per terminal for in/out wiring |
| Strobe certification |
UL Standard 1971 |
| Horn certification |
UL Standard 464 |
| Approvals |
UL, ULC, CSFM certified; FM Approved; MEA (NYC) Acceptance |
Installation notes
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Ceiling current is not wall current: the ceiling-mount appliance draws noticeably more than the wall version at the same candela — 376 mA at 110 cd nameplate rating. Size the NAC from the ceiling figures, not from a wall appliance data point.
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Rate the circuit from the maximum RMS current: the strobe design is constant wattage, so the highest RMS current occurs at the lowest allowable operating voltage, not the highest. The nameplate maximum, not the 24 VDC reference figure, is the number for circuit calculations.
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SmartSync source required: Class B operation requires connection to a compatible SmartSync NAC or to the 4905-9938 SmartSync Control Module. Class A operation requires the 4905-9938 SCM or a compatible panel NAC.
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Thirty-five strobe sync limit: a maximum of 35 synchronized strobes per NAC applies regardless of whether current capacity would allow more.
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Do not exceed 16 VDC at the last appliance: 16 VDC is the lowest voltage allowed at the final appliance on the NAC under worst case conditions. Operation outside the 16 to 33 VDC range can cause permanent damage.
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Surface box coverage: the 4905-9916 red surface mount adapter box extension covers 1 1/2 in. deep surface mounted boxes for ceiling appliances.
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Model number sets the color: unlike the wall-mount A/Vs, ceiling A/V color is not field convertible with a replacement cover — the model number determines the color choice.
Related models
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4906-9130 — the same ceiling-mount A/V in a white housing with red FIRE lettering.
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4906-9127 — the wall-mount version, red housing with white FIRE letters; smaller housing (5 1/8 x 5 x 2 3/4 in.) and lower current draw at every candela setting.
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4906-9129 — wall-mount, white housing with red FIRE lettering.
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4905-9938 — SmartSync Control Module providing Class B or Class A output where the panel NAC does not supply SmartSync directly.
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4905-9927 / 4905-9928 — red wire guard for flush mounted boxes and the adapter plate required to mount that guard to a surface mounted box.
Specifications taken from the Simplex data sheet "SmartSync Operation Audible/Visible Notification with Horn and Synchronized Flash, Non-Addressable," document S4906-0002 Rev. 7 (2/2026). Manufacturer specifications are subject to change without notice.
Documents
FAQ
Can the horn be silenced while the strobe keeps flashing?
Yes. On a two-wire SmartSync circuit the horn operates on-until-silenced while the strobe operates on-until-reset.
What drives SmartSync operation?
Class B needs a compatible SmartSync NAC or the 4905-9938 SmartSync Control Module; Class A needs the 4905-9938 or a compatible panel NAC.
What current should I use for NAC calculations?
The maximum RMS nameplate current: 92 mA at 15 cd, 140 mA at 30 cd, 288 mA at 75 cd and 376 mA at 110 cd.
How many can be synchronized on one NAC?
Up to 35 synchronized strobes per NAC.
