Catch Them Outside,
Not In Your Living Room
An indoor sensor only fires once someone's already inside. Outdoor and curtain detectors move the line of defense out to the yard and the walls — where you actually want it.
Most alarm systems have the same blind spot: they wait. Motion sensors sit inside, watching rooms, and nothing happens until an intruder is already through a door or window and standing in your house. By then the deterrent is late and the response is reactive.
The fix is to detect before entry — out in the yard, along the walls, across the windows. That's what outdoor and curtain detectors do, and they change the whole posture of the system from "catch them inside" to "warn them off outside."
Type One
Outdoor Motion — Watch The Approach
An outdoor motion detector covers an area — a yard, a driveway, the approach to a back door. The old problem with outdoor detection was false alarms: cats, raccoons, a branch in the wind. The Ajax MotionProtect Outdoor ($299) solves that with two sensors working together and software that tells a person from an animal or moving foliage — so it fires on the intruder and ignores the wildlife.
Put one where someone would cross to reach the house, and the system knows there's a person on the approach before a single door is touched. That's the earliest honest warning a system can give.
Type Two
Curtain Detection — A Wall Of Coverage
A curtain detector is different, and clever. Instead of a wide area, it projects a thin, narrow vertical field — a "curtain" — right along a surface: a facade, a run of windows, a fence line. Someone can be out in the yard and not trigger it; the moment they cross that plane to reach a window, they do.
Curtain Outdoor — $289
The Ajax Curtain Outdoor lays a narrow detection curtain along a wall or window run, catching approach at the surface without triggering on the whole yard.
DualCurtain Outdoor — $349
The Ajax DualCurtain Outdoor is bidirectional — one device covers a curtain in two directions along a facade, ideal for protecting a long wall or corner from a single point.
There's an indoor curtain option too: the MotionProtect Curtain ($99) lays the same narrow field along an interior wall of windows or a hallway — useful when you want to guard the glass but let people move through the middle of the room, which pairs naturally with the way group arming lets you protect part of a space.
Why It Matters
Early Detection Enables Active Deterrence
Detecting at the perimeter isn't just about a few extra seconds. It's what makes deterrence possible. When the system knows someone's approaching before they're inside, it can act while they're still outside — sound a siren, light up the yard, bring up a camera. An intruder who trips an indoor sensor is already committed; one caught at the fence line still has every reason to leave.
That's the real argument for perimeter detection: it turns your alarm from something that records what happened into something that tries to stop it happening. We get into exactly how that deterrence works in the companion guide below.
The Options
What It Costs
- MotionProtect Outdoor — $299. Wide-area yard and approach detection, pet- and foliage-immune.
- Curtain Outdoor — $289. A narrow detection curtain along a wall or window line.
- DualCurtain Outdoor — $349. Bidirectional curtain from one device for facades and corners.
- MotionProtect Curtain (indoor) — $99. A curtain field along an interior wall of glass.
Keep Reading
Related Guides
- How many motion sensors you need — why it's fewer than you think
- How a wireless alarm system works — the hub, the sensors, and how it all fits
- Arming your house in parts — protect the perimeter while you live inside
Want The Line Of Defense
At Your Fence, Not Your Couch?
Tell us your property — the yard, the approaches, the vulnerable windows — and we'll design perimeter detection that fires early and false-alarms rarely. Outside is where you want the warning.