How to Install Surface Contacts on Windows and Sliders
Why this matters
A surface contact is the most common device in residential security and the one most often blamed for false alarms. Almost every one of those false alarms comes from placement: a magnet on the frame and the contact on the sash so the wire flexes every time the window moves, a contact jammed against the lock so the customer knocks it loose, a slider contact set where the panel's rattle in its track swings the gap past the operating point. Each window type moves differently, so each gets its own placement, but one rule runs under all of them: the contact (the part with the wire or the battery) goes on the part that does not move, the magnet goes on the part that does, and the closed gap is set small enough that ordinary rattle never reaches the maker's operating gap.
What every installation shares
Contact on the frame, magnet on the sash. The frame is fixed; the sash or panel moves. A wired contact on a moving sash flexes its wire at every opening until the conductor breaks inside the jacket. A wireless contact on a moving sash takes the shocks of every slam on its battery clip and circuit board. The magnet has no wire and no battery and does not care.
Mount where the movement is largest for the least opening. On a hinged sash that is the edge farthest from the hinge. On a sliding sash or panel, any point moves the full opening distance, so choose the spot by what else is there.
Keep clear of the lock and the handle. A contact beside a sash lock gets hit by the hand that works the lock. A contact beside a slider's handle gets hit by every person who opens the door. Six inches of separation from a lock or handle is a common starting point.
The gap. Closed gap is the distance between the magnet and the contact faces with the window shut. The maker gives an operating gap, the separation at which the contact changes state, for a given mounting surface. Set the closed gap as small as the parts allow without touching, so the space between the closed gap and the operating gap absorbs rattle, weatherstrip compression and seasonal movement. Steel frames shorten the operating gap; use contacts rated for steel there. For the contact families and how their ratings differ, see related: Door and Window Contact Types and Gap Ratings.
Fastening. Screws hold best on wood. On vinyl and aluminum, check what is behind the surface: a screw into a hollow vinyl chamber holds poorly and a screw near the glazing can crack the glass or break the insulated glass unit's seal, which fogs the window and is the customer's to replace. Where screws are wrong, the maker's adhesive pad works if the surface is clean: wipe with isopropyl alcohol, let it flash off with the room ventilated and no flame nearby, press firmly, and respect the adhesive maker's minimum temperature. Never screw or drill into the glass, the glazing bead, or the sash's weep holes.
Account on test before any contact on a live monitored system is faulted. See related: How to Put an Alarm Account on Test and Take It Off.
Double-hung windows
The lower sash slides up. Mount the contact on the side jamb (or on the stool or sill where the side jamb is too narrow) and the magnet on the lower sash's side stile or bottom rail, aligned with it. Low on the side jamb, a few inches above the sill, is the usual spot: the meeting rail and its sash lock sit at mid-height, and that is where hands go.
The upper sash. If the upper sash can be lowered and the window is accessible, a second magnet on the upper sash with its own contact, or a contact positioned to see both, covers it. If the upper sash is painted or pinned shut, record that and protect only the lower.
Old wood windows. Pre-1978 sashes and their friction surfaces often carry lead paint. A few screw holes sit below the minor-repair thresholds of the EPA renovation rule (40 CFR 745, Subpart E), but drilling or scraping still produces lead dust: use a HEPA vacuum at the bit and wipe the sill after.
Casement and awning windows
These swing outward on a crank. The edge opposite the hinge moves most, so the magnet goes on the sash's latch-side stile and the contact on the frame beside it. Two complications are specific to the type:
- The screen is inside. A casement's screen sits in the frame inside the sash. The contact and magnet must fit in the space between sash and screen, or the screen will not seat. Measure that space before choosing a contact; slim or recessed contacts exist for exactly this.
- Multi-point locks and the operator. The lock linkage runs along the latch-side stile and the crank operator sits at the sill. Keep the contact above the operator and away from the lock handle's travel.
An awning window hinges at the top; mount at the bottom rail, the edge that moves.
Horizontal sliding windows and sliding doors
Any point on a sliding panel moves the full opening distance, so placement is about the lock, the handle, the track and the rattle. Mount the contact on the latch-side jamb and the magnet on the moving panel's leading edge stile, the edge that meets that jamb when the panel closes, high up, away from the handle and lock.
SLIDING DOOR, INSIDE FACE, LATCH END, TOP OF OPENING
========== head track ===============================
| fixed panel | moving panel | latch-side |
| | | jamb |
| | [ MAGNET ] 1/4 in [CONTACT] |
| | on leading gap on jamb |
| | edge stile, face, |
| | 6 in below facing |
| | head track magnet |
| | | |
| | handle + lock | |
| | at mid-height | |
moving panel opens to the left <--------
The rattle. A slider panel rides on rollers in a track and has a little play, more on an old door with worn rollers. Play along the direction of travel, against the lock, changes the gap between magnet and contact directly; play across the track shifts the faces out of line. Close the gap as far as the trim allows, and choose a contact whose operating gap is comfortably more than the closed gap plus the rattle.
Lift. Some intruders lift a slider panel off its track rather than slide it. A contact high on the leading edge sees that too, because lifting the panel moves the magnet up and away.
The secondary stop. A customer who wants to leave the slider open a few inches for ventilation while armed is asking for a second magnet at the vent position, which tells the panel the door is shut when it is open a few inches. It works, it is their call, and a person can slip through more than they expect; explain it and record the choice.
Worked example: an aluminum patio slider
A 6 ft aluminum slider, moving panel on the right as seen from inside, latch-side jamb on the right. The rollers are original and the panel rattles visibly. The customer wants a wireless contact.
- Placement. Contact on the latch-side jamb face, 6 inches below the head track; magnet on the leading edge stile directly beside it. The handle and lock sit at about 40 inches above the floor, so on an 80 inch door the contact is about 34 inches above the handle.
- Fastening. Aluminum frame, with the glazing channel close to the stile face. Screws were ruled out; adhesive pads after an alcohol wipe, at a room temperature inside the pad maker's range.
- The gap. The trim allows a closed gap of 1/4 inch. With a hand on the panel, it moves back and forth along the track about 1/8 inch against the lock, so the gap ranges from 1/8 to 3/8 inch as it rattles. The contact's sheet gives an operating gap well above that on aluminum, so rattle stays inside the margin.
- Open test. Sliding the panel open slowly with a tape on the stile, the keypad showed the zone faulted at about 5/8 inch of travel and restored on closing. Inside the 1 inch finish test.
- Rattle test. Shaking the closed, locked panel hard in its track for ten seconds, then lifting it against the head: no fault.
- Lift test. With the lock open, lifting the panel as far as the track allows without sliding it: the zone faulted.
What would have gone wrong with the first spot tried. The installer's first instinct was to put the contact at handle height for convenience. The handle is on the leading edge stile at about 40 inches, which would put the magnet a few inches from the handle that every member of the household grabs. On the old rollers the panel also rattles most at mid-height, where the handle is pulled and pushed. High on the stile it moves least and gets touched never.
The finish test, for every window and door
- Faults on opening: before the sash or panel has opened 1 inch at the moving edge.
- Restores on closing: every time, including when the window is closed gently rather than pushed home.
- No trip when rattled: shake the closed, locked sash or panel against its lock for several seconds, push it in and out, and for a slider lift it in the track. The zone stays closed.
- Signal received: with the account on test, the fault and restore appear on the history with the right zone and location name. Once every opening has passed, take the account off test and confirm with the station that it is back to normal.
A contact that passes 1 and 2 and fails 3 will false alarm in wind. Fix the gap now; it will not fix itself. See related: The Alarm That Tripped on Windy Nights.
References
- Contact manufacturer's instruction sheet: operating gap by mounting surface, fastening and adhesive temperature range
- 40 CFR 745, Subpart E, EPA lead renovation, repair and painting rule, for pre-1978 painted sashes
- See related: Door and Window Contact Types and Gap Ratings
- See related: How to Enroll a Wireless Sensor and Confirm Its Signal
- See related: How to Put an Alarm Account on Test and Take It Off