This guide explains how self-diagnostic emergency lights monitor themselves, run automatic tests, and alert you before an outage—so you stay inspection-ready under UL 924 and NFPA 101. Written in plain English for facility managers, contractors, AHJs, and business owners.
Last updated: August 2025
At-a-Glance (What Self-Diagnostics Do)
Microcontroller
- Watches AC power, battery, charger, and lamps 24/7.
- Schedules automatic monthly and annual tests.
- Switches to battery during outages in under 10 seconds.
Battery & Charger
- Smart charging with low-voltage disconnect to protect packs.
- Flags weak/failed batteries and charger faults early.
- Supports Ni-Cd, NiMH, LiFePO4 (model-dependent).
Code Testing
- Monthly 30-second functional test (auto or manual).
- Annual 90-minute duration test verifies runtime.
- Visual status LEDs for pass/fail; keep written logs.
Table of Contents
Microcontroller Logic
The microcontroller is the “brain.” It continuously watches four things: AC input, battery state, charger performance, and lamp circuits. If it sees a problem, it flags a fault with a clear LED signal. It also controls transfer to battery during outages.
How the logic works (plain English)
- Normal mode: AC power present. The charger tops the battery. Status shows steady green.
- Brownout/outage: When AC drops below a safe threshold, the controller transfers to battery (typically within seconds). Lamps come on for egress.
- Protection: A low-voltage disconnect turns lamps off near end of discharge to prevent battery damage.
- Restore: When AC returns, a brief retransfer delay avoids nuisance flicker before charging resumes.
- Self-tests: On a schedule, the controller simulates a power loss for 30 seconds (monthly) and 90 minutes (annually) and watches voltage and lamp current to confirm performance.
Smart charging & energy
- Trickle / pulse charging maintains health without overheat.
- Temperature compensation adjusts charge in hot/cold spaces (model-specific).
- Standby efficiency: Many modern units meet strict battery-charger efficiency rules by reducing standby draw once full.
Battery Checks & Charger Supervision
Self-diagnostic lights supervise both the battery and the charger so you don’t discover a dead pack during an emergency.
What’s monitored
- Connection integrity: Detects unplugged or open-circuit batteries.
- Voltage & capacity: Looks for abnormal sag under load; annual test confirms full 90-minute capacity.
- Charger health: Flags chargers that aren’t delivering expected current/voltage.
- Recharge window: After a long test or outage, verifies the battery fully recharges within the specified time.
Battery chemistries (what you’ll encounter)
Chemistry | Why it’s used | Notes |
---|---|---|
Ni-Cd | Rugged, tolerant of temperature swings | 3–5+ year typical life; easy to service |
LiFePO4 | Long life, light weight, low self-discharge | Great for low-maintenance; heaters for deep cold |
NiMH / Lead-calcium | Higher capacity options | Used when feeding remote heads or long runs |
Monthly 30-Second & Annual 90-Minute Cycles
NFPA 101 requires a brief functional test every month and a full 90-minute test yearly. Self-diagnostic units automate both and report results via status LEDs.
Monthly (30 seconds)
- The controller simulates a power loss; lamps must light and hold steady for ~30 seconds.
- Catches immediate failures (dead lamps, open circuits, loose battery leads).
- You still perform a quick visual check each month and keep a log entry.
Annual (90 minutes)
- Confirms the battery can sustain required illumination for the full 1.5 hours.
- If voltage drops too quickly or lamps dim/fail, the unit logs a battery or lamp fault.
- Afterward, verify recharge and record the test date, results, and any corrective action.
Common Fault Codes (LED Patterns)
Exact patterns vary by brand, but these behaviors are common. When in doubt, count blinks between pauses.
Indicator | Meaning | Action |
---|---|---|
Steady green | Normal; AC present; charging ok | No action |
Blinking green | Self-test in progress | Observe; returns to steady green on pass |
Alt. green/red or amber | High-rate charging / recharge in progress | Allow full recharge; recheck later |
Red – 1 blink | Battery disconnected / open circuit | Check harness/fuse; reconnect/replace battery |
Red – 2 blinks | Battery failure (won’t hold charge) | Replace battery; retest |
Red – 3 blinks | Charger fault | Service/replace charger board |
Red – 4 blinks | Transfer fault (didn’t switch to battery) | Service unit; critical safety issue |
Red – 5 blinks | Lamp circuit fault (lamp out/LED board) | Repair lamp/board; retest |
Tip: Some models show separate labeled LEDs (Battery, Charger, Lamp, AC). Match the lit indicator to the fault and log it.
Maintenance Schedule & Inspection Logs
Monthly (every 30 days)
- Walk-through visual check: steady green, no red/amber faults.
- Spot-test a few units with the push-to-test button (5–10 seconds).
- Log date, pass/fail, and any notes; fix faults promptly.
Annually (every 12 months)
- Verify 90-minute test (automatic or manual group test by circuit).
- Record results and any corrective actions (battery/lamp replacement).
- Confirm recharge within the specified window; recheck indicators next day.
Preventive items
- Batteries: Plan replacements ~3–5 years for Ni-Cd (longer for LiFePO4), or when tests flag capacity loss.
- Cleaning & aiming: Wipe lenses; re-aim heads along egress; secure mounts/wire guards.
- Records: Keep logs for at least 3 years (or per local AHJ policy).
Wet-Location & Harsh-Environment Considerations
For garages, canopies, exteriors, food processing, or cold storage, pick units designed for the environment so self-tests stay meaningful and the unit survives the elements.
What to look for
- Wet Location listing and sealed, gasketed housings.
- IP/NEMA ratings: IP65/IP66 or NEMA 4/4X for wash-down and weather; NEMA 3R for basic outdoor exposure.
- Materials: Corrosion-resistant hardware, UV-stable lenses; tamper-resistant options in public areas.
- Temperature: Cold-weather kits/heaters for freezers; verify minimum/maximum ambient on the spec.
- Hazardous locations: If classified, use units additionally certified (e.g., UL 844 Class/Division as required).
Rule of thumb: NEMA 4X ≈ IP66 protection + corrosion resistance—ideal for outdoor, wash-down, and coastal sites.
Templates & Downloads
Emergency Lighting Schedule & Test Log (CSV)
Columns: Location • Unit ID • Date • Test Type (Monthly/Annual) • Result (Pass/Fail) • Notes • Tech Initials
Maintenance Checklist (CSV)
- Monthly: Visual indicator check; spot push-to-test; log entry
- Annual: 90-minute verification; corrective actions recorded
- Battery replacement plan (by wing/quarter) with dates
- Wet/cold areas: seal checks, heater verification
Visuals & Explainers


Frequently Asked Questions
Do self-testing units satisfy NFPA 101 testing?
Yes. They automate the monthly and annual checks and display pass/fail via LEDs. You still need to perform monthly visual inspections and keep written records.
How long do batteries last?
Ni-Cd commonly 3–5+ years; LiFePO4 often longer. Replace sooner if the unit fails a 90-minute test or shows repeated battery faults.
Can I rely only on the green light?
No. The green light indicates normal charging, but you must confirm that the scheduled tests are happening and that no fault codes are showing—then log it.
What about wet, cold, or classified areas?
Use Wet Location/NEMA-rated units for moisture, cold-weather kits for freezers, and correctly UL 844-rated models for hazardous locations.
Do I need to press the test button if it self-tests?
Not for every unit, every month. Still, many teams spot-check a subset with the push-to-test during the monthly walkthrough.
Visuals & Explainers

Frequently Asked Questions
How long do exit sign batteries last?
Most Ni-Cd packs last 3–5+ years; LiFePO4 can last longer. Replace sooner if the unit fails a 90-minute test.
Do self-testing signs satisfy NFPA 101 testing?
Yes—self-testing can automate the required monthly/annual checks. You still need to maintain and retain test records.
What does “remote-capable” mean?
The exit sign’s battery can power additional remote emergency lamp heads. Confirm total wattage vs. runtime math.
Red vs. green letters—does it matter?
Both are code-accepted; verify local preferences (e.g., healthcare design) and maintain consistency across a facility.
What’s the difference between Wet Location and NEMA 4X?
Wet Location means the unit is listed for water exposure; NEMA 4X adds dust-tight and corrosion resistance for harsher sites.
Can I use a standard sign in a freezer?
No—use a cold-weather rated model with a battery heater and a verified minimum operating temperature on the spec sheet.
Tools & Calls-to-Action
Remote-Head Load Calculator
Enter lamp wattage and count to size a remote-capable battery for 90-minute runtime.
Spec Review
Upload your environment and constraints (cold, wet, haz-loc) for a short-list of compliant models.
Talk to a Code Specialist
Get help mapping UL 924, NFPA 101 testing, and local AHJ expectations to your facility layout.