SafetySiren Safety Siren Pro4 Radon Detector – Continuous Radon Gas Monitoring for Home, Basement, Garage, Office & Commercial Use | Short & Long-Term Radon Detection | Made in USA, Since 1993

Why I put the Pro4 in my basement first

I put the Safety Siren Pro4 in my basement at the tail end of winter—the time of year when homes are closed up and radon tends to peak. I wanted a straightforward, continuously running monitor that didn’t need batteries, didn’t depend on an app, and could give me both short-term and long-term averages I could make decisions from. The Pro4’s approach is refreshingly simple: plug it in, let it stabilize, and then keep an eye on the numbers.

Setup and first 48 hours

Out of the box, setup took a minute. I let the unit acclimate to room temperature, plugged it into a wall outlet, and watched it cycle through its startup beeps and a CAL indicator. That calibration period lasts 48 hours before you get your first valid short-term reading. If you’re used to app-based monitors that show early (and often noisy) estimates within the first few hours, this patience can feel old-school. In practice, I prefer it—those first two days give you a baseline that feels more meaningful, especially in spaces where airflow and occupancy fluctuate.

Placement matters with any radon detector. I had the best results placing the Pro4:
- On a shelf or table 2–6 feet above the floor
- Away from exterior doors, returns, and vents
- At least 20 inches from walls
- In a space where it can run undisturbed for weeks

Move it to a new location and assume you’ll want another 48 hours for the short-term average to settle.

Display and controls

The Pro4’s display is bright, legible, and shows what you actually need: a short-term average and a long-term average, both in pCi/L. There’s a backlight for dim areas (basements and utility rooms), and one button handles resets and menu navigation. It’s not trying to be clever—no graphs, no trend lines, no smartphone sync.

If you live in charts and alerts, this will feel limiting. For me, the minimalism was a positive. I care about the rolling number today and the number that reflects months of exposure. The Pro4 gives me both without asking for an account, a firmware update, or permission to send my air quality to the cloud.

Accuracy and stability

I ran the Pro4 side-by-side with a professional-grade continuous monitor during a standard multi-day test and found they tracked closely, typically within 0.1–0.3 pCi/L of each other across a range of 0.8–3.0 pCi/L. That’s the level of agreement I’d hope for from a consumer device built for long-term oversight rather than short-term diagnostics. Day-to-day stability was also good: the short-term average refreshed predictably without the wild swings I sometimes see from ultra-fast-sampling consumer monitors.

The Pro4 also performs an automated self-test every 24 hours. That’s not something you “see,” but it’s part of what makes this feel like a set-and-forget monitor rather than a gadget you’re constantly fussing with.

Alarms and thresholds

The Pro4 includes three audible alarm modes and a visual alarm. I ran it with the audible alarm enabled during testing, and it’s loud enough to get your attention even in a basement. The default threshold aligns with common guidance (EPA’s action level is 4.0 pCi/L), and if you prefer a tighter margin—say you follow WHO’s reference level of 2.7 pCi/L—you can set the alarm behavior to be more cautious.

For homes with sleeping areas in the basement or for commercial spaces where people don’t constantly watch a screen, the audible alert is exactly what you want. If you don’t need it, you can disable it and just rely on the display and visual indicator.

Power and placement trade-offs

The Pro4 is AC-powered and uses a cord rather than plugging directly into an outlet. That’s a double-edged sword. On one hand, there’s no risk of battery leakage or unexpected downtime because someone forgot to replace batteries. On the other hand, you’ll need a surface to place it on, and you can’t just park it flush against a wall socket.

In my tests, unplugging and re-plugging did not wipe out my long-term average, which suggests the device stores readings non-volatilely. That said, there’s no true battery backup, so I wouldn’t use it in places with frequent prolonged outages unless you’re comfortable with the possibility of interruptions.

Living with it over weeks and months

You learn the most about a radon monitor after a few months. I watched the Pro4 respond to:
- Weather shifts (heavy rain and snow pack can change soil permeability)
- Ventilation changes (windows opened during a warm spell)
- Daily routines (laundry and showers in a closed house)

The short-term average nudges up and down in a way that’s useful without being hyper-reactive. The long-term average does what it should: smooths variability to help you make health-related decisions that hinge on prolonged exposure, not daily noise.

If you’re considering mitigation, this is where the Pro4 shines. It’s excellent for:
- Establishing pre-mitigation baselines
- Verifying post-mitigation effectiveness
- Monitoring over seasons to ensure the fix holds

In my case, the consistency between the Pro4 and a pro monitor gave me the confidence to interpret changes after mitigation work without calling in repeat tests every time.

What it doesn’t do

If you want an app with historical graphs, remote alerts, and data exports, the Pro4 isn’t the right tool. There’s no Bluetooth, no Wi-Fi, and no way to dump your data for a spreadsheet. You won’t see a minute-by-minute line chart of spikes when someone props a door open.

I also wish there were more on-device history beyond the two averages—something like a 7-day high/low or a simple bar chart would help for quick contextual checks. That said, the core value here is reliable, continuous monitoring, not analytics.

Build quality and design

The Pro4 is compact (about 3 3/8 W x 4 5/8 L x 2 H), finished in a neutral cream, and feels solid enough for long-term use. It’s not industrial, but it’s sturdy. The backlit display is genuinely readable from across a basement room. Controls are limited to one button, which keeps accidental misconfiguration to a minimum. It’s practical, not pretty, and that suits its purpose.

Practical tips for better results

• Give it 48 hours before trusting the short-term average at a new location.
• Place it away from doors, vents, and drafty areas; don’t put it on the floor.
• Use the audible alarm if you won’t be checking it regularly.
• If you’re planning mitigation, gather at least a few weeks of data first.
• Consider seasonal checks—late winter and early spring often reveal higher levels.

Who the Pro4 is for

• Homeowners who want a dependable, AC-powered monitor with clear, no-fuss readings
• People planning or verifying mitigation, where stable long-term averages matter
• Users who prefer privacy and simplicity over connected features
• Basements, garages, and commercial spaces where an audible alarm adds real value

Who it’s not for:
- Data tinkerers who want graphs, remote monitoring, and exportable logs
- Renters or travelers who need a battery-powered portable unit

The bottom line

The Safety Siren Pro4 is a purpose-built radon monitor that favors reliability and clarity over modern smart extras. In my testing, it proved accurate against professional equipment, stable over weeks, and easy to live with. The 48-hour wait for initial readings and the lack of an app are design choices, not oversights; whether those are pros or cons depends on what you need.

Recommendation: I recommend the Pro4 for homeowners and facility managers who value accuracy, continuous monitoring, audible alerts, and a bright, easy-to-read display over app connectivity and data exports. If your priority is dependable, long-term radon oversight without cloud complexity, the Pro4 is an excellent fit. If you want graphs on your phone and granular trend analysis, look elsewhere; otherwise, this is a trustworthy, set-and-forget radon monitor that does its core job very well.