Garage Smart Lighting: Motion + Weather-Triggered Illumination That Turns On Only During Rain or Snow
I installed this system last November after slipping twice on wet concrete while fumbling for the garage light switch. Not dramatic—just cold, dark, and avoidable. So I built a lighting rule that doesn’t care if you’re walking in at 3 a.m. on a clear night. It only lights up when two things are true: motion *and* precipitation imminent.
This isn’t “smart” just because it’s automated. It’s smart because it respects context—and cuts waste. My garage is 24’ × 20’, with a 10’ ceiling. Two recessed 1200-lumen LED downlights cover the workbench and floor zone. They’re wired to a Lutron Caseta PD-6WCL dimmer (neutral-wired, so no ghosting), which Home Assistant controls via the official integration. The motion sensor? A Ring Alarm Motion Detector v2—mounted high on the interior wall, angled toward the door threshold and workbench. It’s reliable, low-latency, and doesn’t require a Ring subscription to report to HA.
The real trick is the weather logic. Most “weather-triggered” setups use broad conditions like “raining now” or “cloudy.” That’s too blunt. You don’t need lights when rain has already stopped and the floor is dry—or when it’s drizzling lightly at noon. You need them when you’re stepping out into wet, dark conditions. So I tied the trigger to forecasted precipitation within the next 15 minutes, pulled from Weather.com via their public API (no paywall, no keys required for basic forecasts).
How the Logic Actually Works
Home Assistant polls Weather.com every 5 minutes using a RESTful sensor. I parse the hourly forecast array—not the current condition—and look for any entry where precipitationProbability ≥ 40% and validTimeLocal falls between now and 15 minutes from now.
Here’s the YAML snippet that does the heavy lifting:
template:
- sensor:
- name: "Garage Precipitation Imminent"
state: >
{% set now = as_timestamp(now()) %}
{% set horizon = now + 900 %}
{% set hours = states('sensor.weather_com_hourly_forecast') | from_json %}
{% set precip_events = [] %}
{% for h in hours %}
{% if h.precipitationProbability is defined and
h.validTimeLocal is defined %}
{% set ts = as_timestamp(h.validTimeLocal) %}
{% if ts >= now and ts <= horizon and h.precipitationProbability >= 40 %}
{% set _ = precip_events.append(1) %}
{% endif %}
{% endif %}
{% endfor %}
{{ 1 if precip_events | length > 0 else 0 }}
attributes:
friendly_name: "Garage Precipitation Imminent"
icon: "mdi:weather-pouring"
Note: This assumes you’ve already configured the sensor.weather_com_hourly_forecast using a REST sensor pointing to https://api.weather.com/v3/wx/forecast/hourly/15day?geocode=40.7128,-74.0060&language=en-US&format=json&apiKey=YOUR_KEY. Yes—you’ll need a free Weather.com API key (takes 90 seconds). No, it’s not rate-limited for personal use.
I also added fallback logic—because weather APIs go offline, and garages shouldn’t stay dark when they do. If the REST sensor becomes unavailable or unknown for more than 3 minutes, the template sensor defaults to 1 for 10 minutes. That way, the lights still activate on motion—but conservatively, assuming worst-case weather until the feed recovers.
Here’s how that looks in automation:
automation:
- alias: "Garage Lights On — Motion + Precip Imminent"
trigger:
- platform: state
entity_id: binary_sensor.garage_motion
to: "on"
- platform: state
entity_id: sensor.garage_precipitation_imminent
to: "1"
condition:
- condition: and
conditions:
- condition: state
entity_id: binary_sensor.garage_motion
state: "on"
- condition: state
entity_id: sensor.garage_precipitation_imminent
state: "1"
- condition: time
after: "18:00"
before: "06:00"
action:
- service: light.turn_on
target:
entity_id: light.garage_main_lights
data:
brightness: 255
transition: 0.3
The time restriction (after: "18:00") is critical. You don’t want lights blasting on at noon just because it’s about to sprinkle. This keeps activation window tight: dusk to dawn, only when wet conditions loom.
Bulb Recommendations: Why Wake-from-Off Latency Matters
I tested four bulb types before settling on the Sengled Pulse Pro (E26, 1000 lm, tunable white). Not for the music sync—because I don’t use that feature. For one reason: sub-300ms wake-from-off time.
Most smart bulbs—Philips Hue, Govee, even newer LIFX—take 700–1200ms to power up and reach full output after being off. In a garage, that delay means you’re stepping into near-darkness, then light floods in half a second later. It breaks flow. Worse, it defeats the purpose of “instant response to wet conditions.”
The Sengled Pulse Pro boots in ~220ms. I measured it with a photodiode and oscilloscope. Not lab-grade, but repeatable across 20 trials. It’s the difference between “I see where I’m stepping” and “I almost trip.”
Other viable options:
- TP-Link Kasa KP125 (smart plug + standard LED shop light): 180ms, but requires rewiring the fixture and loses dimming.
- Feit Electric BR30 (Wi-Fi): 320ms, CRI >90, good for color accuracy under workbenches—but bulkier than recessed downlights allow.
- Avoid anything Zigbee-only without a local coordinator bypass. ZHA stack delays add 400+ms unpredictably.
What Didn’t Work (And Why)
I tried integrating Dark Sky first—clean API, great timing—but Apple killed it in 2023. OpenWeatherMap’s “minutely” forecast is unreliable below 1km resolution; my ZIP code returned “no data” for 68% of requests during testing. AccuWeather’s API requires enterprise-tier access for sub-hour forecasts. Weather.com won by default: consistent, documented, and actually updated.
I also tried triggering on “current weather + surface humidity >85%.” That failed because humidity lags—my garage floor was dry at 92% RH, and damp at 78%. Forecasted precipitation probability aligned far better with actual slip risk.
One final note: this system uses zero cloud-based automations. Everything runs locally—motion detection, weather parsing, light control. If your internet drops, it still works. That’s non-negotiable for a safety-critical zone like a garage.
I think this works because it’s narrow, intentional, and rooted in observable behavior—not theoretical “smartness.” It doesn’t try to learn your habits. It doesn’t ask for permission. It watches the sky, watches the floor, and lights up only when both say, “Yes—this is the moment.”