Most Ring and SimpliSafe entry sensors go up in five minutes — peel the backing, press it to the frame, done. But on a lot of real-world doors, that’s where the trouble starts. Decorative molding, deep trim, recessed door panels, and older construction can all push the two sensor pieces far enough apart that the system can’t tell whether the door is open or closed. The result is false alarms, missed alerts, or a sensor that reads as permanently open.
This guide covers exactly that problem: what causes the gap issue, what the actual detection limits are for Ring versus SimpliSafe, and how to fix it cleanly without drilling into anything.
Ring vs. SimpliSafe: The Detection Gap Is Not the Same
This is the part that trips people up most often, and it’s worth getting right before you touch anything else.
Ring and SimpliSafe have different maximum detection gaps, and if you’re working from memory or from older guides, you may have the wrong number in your head.
| System | Max Detection Gap | Official Riser Available |
|---|---|---|
| Ring Alarm Contact Sensor (2nd Gen) | 1 inch (2.5 cm) | Yes |
| SimpliSafe Entry Sensor | 2 inches | Third-party only |
Ring’s limit is tighter. If you have a Ring sensor and the gap between the sensor body and the magnet is more than one inch when the door is fully closed, the sensor will not work correctly. SimpliSafe gives you a bit more room at two inches, but that still isn’t much on a door with raised molding or a thick frame profile.
Before you mount anything, close the door and hold both sensor pieces in their intended positions. Measure the gap. That number tells you whether you have a problem and, if so, how big a riser you need to correct it.
Why the Gap Problem Happens
Entry sensors are designed for flat, flush door and frame combinations. In that scenario, both pieces sit right next to each other when the door closes and the gap is negligible. The problem shows up when the mounting surfaces aren’t on the same plane.
A few common causes:
The door frame has raised or layered trim. Ornate molding adds depth, which means the sensor mounted on the frame sits farther away from the door surface than a flat installation would.
The door sits recessed in the frame. On some exterior doors and older construction, the door itself sits back from the face of the trim, creating a natural gap that has nothing to do with how you mount the sensor.
The window sash doesn’t close flush with the frame. Double-hung windows are frequent offenders here, especially in older homes where the frames have settled or swelled.
The sensor is mounted on the wrong side of the molding profile. This one is fixable without a riser, sometimes, just by repositioning.
The Fix: Sensor Risers
A riser is a small block that mounts between the sensor and the surface it’s attached to, raising it out toward the opposite piece so both halves end up within the required detection distance. The concept is simple and the products are inexpensive. The tricky part is knowing which riser to buy, because Ring and SimpliSafe use different hardware and the riser options work differently.
For Ring sensors: the official riser
Ring makes its own riser for the Contact Sensor 2nd Gen. It’s a slide-on plastic bracket, not adhesive. The sensor body clips into it, adding about 10mm of height. The kit also includes a taller magnet to use on the other side of the door or window, so both pieces gain elevation proportionally.
The Ring Alarm Contact Sensor Riser (2nd Gen) is the right part. A couple of things to keep in mind: this riser only works with the 2nd generation Ring Contact Sensor, and because it slides onto the sensor body, you’ll need to remove it any time you’re changing the battery. That’s a minor inconvenience, but worth knowing before you tuck the sensor behind a tight piece of molding.
For SimpliSafe sensors: adhesive risers
SimpliSafe doesn’t sell an official riser, but third-party options are widely available and work well. These are adhesive foam or plastic blocks that attach to the door surface, with the sensor then mounting on top. They come in different heights, so you can match the riser height to the gap you measured.
The Security Sensor Riser for SimpliSafe Entry Sensors is a solid option. It attaches with an included 3M adhesive strip and the sensor mounts directly to it using its existing adhesive backing. No tools required.
Adhesive vs. Screws: Which Should You Use
Once the gap issue is resolved, you still need to decide how to attach the sensor. Both Ring and SimpliSafe include two attachment options in the box: an adhesive pad already applied to each piece, and a small set of mounting screws with hardware.
For most applications, adhesive is the faster and cleaner choice. It leaves no holes, and if you ever need to reposition the sensor, removal is easy.
There is one situation where screws are worth the extra two minutes: flat or matte paint. The adhesive included with both systems grips poorly to flat paint, which is extremely common on interior door frames in newer construction. If you’ve ever had a sensor drop off the wall at 2am and trigger an alarm, this is almost certainly why. On any surface with flat or matte paint, use the screws. On semi-gloss or glossy surfaces, the adhesive performs reliably.
One additional note for Ring: if you’re using the official slide-on riser, the sensor mounts to the riser, not directly to the surface, so the attachment point is the riser-to-wall connection. Use the adhesive included with the riser for that bond.
Windows: Same Problem, Sometimes Worse
The gap issue is as common on windows as it is on doors, and on certain window types it can be more difficult to solve.
Double-hung windows are the most frequent problem. The sash, which is the part that moves, sits in a channel, and when closed, the gap between the sash face and the surrounding frame can easily exceed the detection limit depending on the window’s age and how the trim is built out.
Casement windows, which crank open on a hinge, can also present unusual mounting angles where the sensor and magnet end up offset vertically rather than just spaced apart.
For either type, the riser solution applies. Mount the riser to the sash, place the sensor on the riser, and put the magnet on the fixed frame. Test with the window fully closed before committing to a final position.
A few window-specific notes:
Check that neither piece sits in a spot where it would get pinched or crushed when the window fully closes. This is easy to overlook during test fitting when the sensor is loose.
On double-hung windows, the bottom sash is the one that moves most often. Mount accordingly.
Garage Doors and Shed Doors
Applying a contact sensor to a garage door or outbuilding introduces a different version of the gap problem. Most garage doors aren’t flat across the face, and the door panel surface and the frame it sits against when closed are rarely on the same plane. The gap can easily exceed an inch, and the surfaces involved, painted metal, vinyl, or rough wood, don’t always hold adhesive well.
For garage doors, dedicated mounting brackets designed for Ring and SimpliSafe sensors are available and handle the alignment issue more cleanly than a riser block in this application. Look for the specific garage door bracket for your sensor model rather than adapting an interior door riser.
On shed doors and gates, the surface materials are often rougher and the door may flex slightly in use. Use screws rather than adhesive in these locations, and check that the sensor and magnet are still aligning correctly after the door has been opened and closed several times.
Troubleshooting: Sensor Shows Open When Door Is Closed
If the sensor is already mounted and reads as open even when the door is shut, work through these in order before assuming the sensor is defective.
The gap is too large. This is the most common cause. Measure the actual distance between the two pieces with the door closed. If it’s over the limit for your system, a riser is the fix.
The pieces aren’t aligned. The sensor and magnet need to be roughly parallel and facing each other. If one piece is rotated or offset significantly from the other, the magnetic connection can fail even within the distance limit. Reposition so they’re directly across from each other.
The magnet is on a metal surface. Metal can interfere with the magnetic signal. If your door has a steel core or the mounting area is close to a metal frame component, try relocating both pieces a few inches away from the metal.
The adhesive has failed and one piece has shifted. This is more common than people expect, especially on flat-painted surfaces. Check that both pieces are still firmly seated. If the adhesive has given out, clean the surface with rubbing alcohol and switch to screws.
The sensor needs to be re-paired. If none of the above resolves it, try removing and re-adding the sensor in your Ring or SimpliSafe app. A pairing issue can occasionally cause a persistent open reading that has nothing to do with physical placement.
