DH-35 Recessed Wired Door Contact – NC Magnetic Reed Switch Sensor

The DH-35 Recessed Door Contact Sensor (NC) is a wired magnetic security sensor designed to detect door or window openings in alarm and security systems.

This model uses a magnetic reed switch and magnet pair. When the door is closed, the magnet keeps the circuit closed. When the door opens and the magnet moves away, the circuit breaks and sends a signal to the alarm panel. Magnetic reed switches are commonly used in security systems because they reliably change electrical contact when a magnetic field is removed.

The recessed installation design allows the sensor and magnet to be hidden inside the door frame, making the system more secure and visually discreet. Recessed magnetic contacts are widely used in alarm and access control systems where a clean installation is preferred.

The DH-35 sensor is ideal for wooden doors, windows, cabinets, and entry points in residential and commercial security installations.

A recessed contact disappears into the door. The DH-35 is a recessed magnetic reed switch sensor, meaning both halves are drilled into the door and frame rather than screwed onto the surface. Once the door is closed the sensor is completely invisible. That matters for two reasons: it looks far better on a good quality door, and an intruder cannot see, reach, or tamper with a contact they do not know is there.

Recessed or surface mount, how to choose. Surface mount contacts screw onto the frame and take two minutes to fit, which makes them right for retrofitting, for metal doors you would rather not drill, and for anywhere appearance does not matter. Recessed contacts like this one need a drilled hole in the door edge and frame, so they suit new installations, quality wooden doors, and any situation where you want the security system to be discreet. If you are fitting an alarm in a home you care about the look of, recessed is worth the extra work.

Where it is normally used. Main entrance doors, bedroom and study doors, office doors, and internal doors in homes and offices across Pakistan where a wired alarm system is being installed. It is a standard component in almost every professional intruder alarm installation.

NC contact and why alarms use it. This is a normally closed contact. With the door shut, the circuit is complete and current flows. Opening the door breaks that circuit and signals the panel. The important consequence is that cutting the cable produces exactly the same result as opening the door, so an intruder cannot quietly disable the sensor by snipping the wire. This is why NC is the standard for security work and why you should be cautious of any installer fitting NO contacts on an alarm zone.

Fitting it properly. Drill the frame for the sensor body and the door edge for the magnet, positioning both so they align precisely when the door is closed. Mount on the hinge side edge where practical, because that part of the door moves least and stays most consistently aligned. Keep the closed gap within the sensor’s rated distance, which is a small number of millimetres. Take care drilling depth on a hollow core door, and check alignment again a few weeks later.

Why doors stop reporting correctly. Almost every fault we are asked about turns out to be alignment rather than a failed sensor. Wooden doors swell in monsoon humidity and shrink in dry heat, so a contact fitted with no margin in April can drift out of range in August. Fitting with the two halves properly centred rather than at the edge of tolerance prevents most seasonal problems.

Wiring into your alarm panel. Run the cable from the frame side, in conduit, back to the panel and terminate it on a zone with the correct end of line resistor if your panel monitors for tampering. Never run cable to the moving leaf of the door. Label the cable at the panel end so future maintenance is straightforward.

No batteries, no internet. A wired reed contact draws its power from the alarm panel, so there is nothing to replace and nothing to go flat. It does not rely on WiFi, a router, or an internet connection, which means it keeps protecting the door during load shedding as long as the panel has its backup battery. That independence is the main argument for wired sensors over wireless ones on doors that genuinely matter.

How many doors should you cover? Every external door and any internal door protecting something valuable. Contacts are inexpensive relative to the rest of an alarm system, and a door left uncovered is simply the door an intruder will use.

Will it fit my door? It needs enough thickness in the door edge and frame to accept the drilled body. Very thin or hollow doors may suit a surface mount contact better. Send a photograph and measurement and we will confirm.

Can I use it on a metal door? Metal affects magnetic fields and drilling steel is harder work. For metal doors we usually recommend a surface mount or dedicated metal door contact instead.

Does it work with any alarm panel? Yes, any panel that accepts standard NC zone inputs, which covers essentially all conventional intruder alarm panels.

What is the difference between this and the DH-36? Both are recessed reed contacts; they differ in body size and operating gap. Tell us your door and we will confirm which suits it.

Buying from ZZ Marts. In stock at our Karachi (Saddar) and Lahore stores with nationwide delivery, supplied by Zam Zam Traders, trading in security hardware since 2005. We also stock surface mount contacts, rolling shutter contacts, wireless Tuya door sensors, alarm panels, sirens, and cabling. Tell us how many doors you are covering and we will quote the sensors, panel, and cable together.