{"product_id":"door-magnetic-sensor-102-aluminium","title":"DH-55 Metal Door Contact – NC \u0026 NO\/NC 3-Wire Magnetic Sensor","description":"\u003cul\u003e\r\n \t\u003cli data-start=\"221\" data-end=\"286\"\u003e\r\n\u003ch2 data-start=\"338\" data-end=\"359\"\u003e\u003cstrong data-start=\"341\" data-end=\"359\"\u003eKey Features\u003c\/strong\u003e\u003c\/h2\u003e\r\n\u003cul data-start=\"360\" data-end=\"948\"\u003e\r\n \t\u003cli data-start=\"360\" data-end=\"458\"\u003e\r\n\u003cp data-start=\"362\" data-end=\"458\"\u003e\u003cstrong data-start=\"362\" data-end=\"389\"\u003eTwo Variants Available:\u003c\/strong\u003e\u003cbr data-start=\"389\" data-end=\"392\"\u003e– NC magnetic reed switch\u003cbr data-start=\"419\" data-end=\"422\"\u003e– NO\/NC 3-wire universal contact\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n \t\u003cli data-start=\"459\" data-end=\"554\"\u003e\r\n\u003cp data-start=\"461\" data-end=\"554\"\u003e\u003cstrong data-start=\"461\" data-end=\"490\"\u003eHeavy-Duty Metal Housing:\u003c\/strong\u003e Designed for industrial and commercial security applications.\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n \t\u003cli data-start=\"555\" data-end=\"645\"\u003e\r\n\u003cp data-start=\"557\" data-end=\"645\"\u003e\u003cstrong data-start=\"557\" data-end=\"594\"\u003eStrong Magnetic Trigger Distance:\u003c\/strong\u003e Reliable detection even on large or heavy doors.\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n \t\u003cli data-start=\"646\" data-end=\"742\"\u003e\r\n\u003cp data-start=\"648\" data-end=\"742\"\u003e\u003cstrong data-start=\"648\" data-end=\"679\"\u003eSecure Wired Communication:\u003c\/strong\u003e Ensures stable alarm signal with zero wireless interference.\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n \t\u003cli data-start=\"743\" data-end=\"846\"\u003e\r\n\u003cp data-start=\"745\" data-end=\"846\"\u003e\u003cstrong data-start=\"745\" data-end=\"774\"\u003eMounts to Metal Surfaces:\u003c\/strong\u003e Ideal for metal doors, shutters, gates, and industrial access points.\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n \t\u003cli data-start=\"847\" data-end=\"948\"\u003e\r\n\u003cp data-start=\"849\" data-end=\"948\"\u003e\u003cstrong data-start=\"849\" data-end=\"887\"\u003eWorks With Alarm \u0026amp; Access Systems:\u003c\/strong\u003e Compatible with panels, maglocks, relays, and controllers.\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n\u003c\/ul\u003e\r\n\u003c\/li\u003e\r\n\u003c\/ul\u003e\n\n\u003cul\u003e\r\n \t\u003cli data-start=\"221\" data-end=\"286\"\u003e\r\n\u003cp data-start=\"991\" data-end=\"1315\"\u003eThe \u003cstrong data-start=\"995\" data-end=\"1023\"\u003eDH-55 Metal Door Contact\u003c\/strong\u003e is a durable wired magnetic sensor designed for demanding security applications. It features a reinforced metal housing that withstands impact and stress, making it suitable for commercial entrances, warehouse doors, rolling shutters, gates, and industrial areas where plastic contacts fail.\u003c\/p\u003e\r\n\u003cp data-start=\"1317\" data-end=\"1355\"\u003eTwo wiring variations are available:\u003c\/p\u003e\r\n\r\n\u003cul data-start=\"1357\" data-end=\"1561\"\u003e\r\n \t\u003cli data-start=\"1357\" data-end=\"1445\"\u003e\r\n\u003cp data-start=\"1359\" data-end=\"1445\"\u003e\u003cstrong data-start=\"1359\" data-end=\"1373\"\u003eNC Contact\u003c\/strong\u003e – Circuit remains closed when door is shut and opens when door opens.\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n \t\u003cli data-start=\"1446\" data-end=\"1561\"\u003e\r\n\u003cp data-start=\"1448\" data-end=\"1561\"\u003e\u003cstrong data-start=\"1448\" data-end=\"1472\"\u003eNO\/NC 3-Wire Contact\u003c\/strong\u003e – Provides universal configuration to support both wiring needs using a single sensor.\u003c\/p\u003e\r\n\u003c\/li\u003e\r\n\u003c\/ul\u003e\r\n\u003cp data-start=\"1563\" data-end=\"1767\"\u003eThe strong magnetic trigger ensures stable detection even with vibration or heavy metal doors. It integrates easily with alarm panels, access control systems, CCTV alarm inputs, and smart relay modules.\u003c\/p\u003e\r\n\u003cp data-start=\"1769\" data-end=\"1896\"\u003eDesigned for high-security environments, the DH-55 offers long-term reliability and dependable intrusion detection performance.\u003c\/p\u003e\r\n\u003c\/li\u003e\n\u003c\/ul\u003e\r\n\r\n\u003c!--zzmv2--\u003e\r\n\u003ch3 style=\"font-size:1.15em;font-weight:600;line-height:1.4;margin:1.6em 0 .4em;\"\u003eA metal door contact with three wire flexibility\u003c\/h3\u003e\r\n\u003cp\u003eThe DH-55 is a surface mount magnetic contact built specifically for metal doors, and supplied in a three wire configuration offering both normally closed and normally open outputs. That combination is what sets it apart: one sensor can signal an alarm panel and, at the same time, drive a second device such as a relay, indicator, or automation input.\u003c\/p\u003e\r\n\u003ch3 style=\"font-size:1.15em;font-weight:600;line-height:1.4;margin:1.6em 0 .4em;\"\u003eWhy metal doors need a purpose built contact\u003c\/h3\u003e\r\n\u003cp\u003eSteel and aluminium distort magnetic fields, which is why an ordinary plastic door contact often behaves unpredictably when fitted to a metal door or frame. It may fail to detect closure, or report the door open when it is shut. A contact designed for metal doors accounts for this, and is housed to survive the knocks that steel doors and their surroundings tend to deliver.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eWhere it is fitted.\u003c\/strong\u003e Factory and warehouse steel doors, godown entrances, metal framed commercial doors, plant rooms, and any hard working door where a standard plastic contact has already cracked or proved unreliable.\u003c\/p\u003e\r\n\u003ch3 style=\"font-size:1.15em;font-weight:600;line-height:1.4;margin:1.6em 0 .4em;\"\u003eUnderstanding the three wire NO and NC output\u003c\/h3\u003e\r\n\u003cp\u003eA two wire contact gives you one circuit. This three wire version provides a common plus both a normally closed and a normally open contact, so you can choose either behaviour, or use both at once. The practical value is flexibility: wire the NC side into your intruder alarm zone for security, and use the NO side to trigger something else, such as a relay module switching on a light, an indicator lamp at a guard desk, or an input to a building automation controller. If you only need a simple alarm connection, use the NC pair and leave the third wire unused.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eWhy alarms use the NC side.\u003c\/strong\u003e With a normally closed circuit, current flows continuously while the door is shut. Opening the door breaks the circuit and triggers the alarm, and so does cutting the cable. That means an intruder cannot quietly defeat the sensor by snipping the wire, because doing so produces the same alarm as opening the door. This is the standard configuration for security work.\u003c\/p\u003e\r\n\u003ch3 style=\"font-size:1.15em;font-weight:600;line-height:1.4;margin:1.6em 0 .4em;\"\u003eMounting on steel correctly\u003c\/h3\u003e\r\n\u003cp\u003eFit the sensor body to the fixed frame and the magnet to the door, directly opposite one another rather than at an angle. If detection is inconsistent, mount both halves on thin non metallic spacers so they sit slightly proud of the steel, which reduces the interference the metal causes. Keep the closed gap comfortably inside the rated operating distance rather than at its outer limit, leaving margin for the door settling over time.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eAlignment causes most faults.\u003c\/strong\u003e When a door contact starts misreporting, alignment has usually drifted rather than the sensor having failed. Heavy steel doors drop on their hinges with use and frames move with heat. Fit the halves centred, and check again a few weeks after installation once the door has settled into its daily pattern.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eCabling.\u003c\/strong\u003e Run cable to the fixed frame side, never to the moving leaf, and keep it inside conduit. On an industrial door an exposed sensor cable is both a maintenance problem and an obvious point of attack. Label all three cores at both ends, because a three wire contact is considerably easier to work on later if someone has recorded which core is common, which is NC, and which is NO.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eNo batteries, no internet dependency.\u003c\/strong\u003e Being wired, the contact draws power from the panel or circuit it serves, so there is nothing to replace and nothing to go flat unnoticed. It needs no WiFi, router, or internet connection, so the door remains monitored through load shedding as long as the panel has its backup battery. On a commercial door protecting stock or plant, that independence is the entire argument for wired over wireless.\u003c\/p\u003e\r\n\u003ch3 style=\"font-size:1.15em;font-weight:600;line-height:1.4;margin:1.6em 0 .4em;\"\u003eChoosing between our door contacts\u003c\/h3\u003e\r\n\u003cp\u003eSee our full range of \u003ca href=\"\/collections\/door-sensors-relay-modules\"\u003edoor sensors and relay modules\u003c\/a\u003e to compare recessed, surface mount and rolling shutter options. Use this DH-55 for metal doors, and where you want both NO and NC outputs from one sensor. Use the recessed DH-35 or DH-36 where you want an invisible, tamper resistant contact on a quality wooden door. Use the DH-58 rolling door contact for steel shutters, where the gap is wide and inconsistent. Use the DH-32 surface mount for straightforward retrofits. Use a wireless Tuya sensor where you want phone alerts and cannot run cable.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eDo I have to use all three wires?\u003c\/strong\u003e No. Use the common and NC pair for a standard alarm connection and leave the NO core unconnected and insulated.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eWill it work on an aluminium framed glass door?\u003c\/strong\u003e Yes, this is a common application, using spacers if detection proves marginal.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eDoes it need its own power supply?\u003c\/strong\u003e No. It is powered by the alarm panel or circuit it connects to.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eCan it be used outdoors?\u003c\/strong\u003e Fit it in a sheltered position. For fully exposed installations tell us and we will recommend a suitably rated alternative.\u003c\/p\u003e\r\n\u003cp\u003e\u003cstrong\u003eBuying from ZZ Marts.\u003c\/strong\u003e Available at our \u003ca href=\"\/pages\/karachi-store\"\u003eKarachi store\u003c\/a\u003e and \u003ca href=\"\/pages\/lahore-store\"\u003eLahore store\u003c\/a\u003e, and typically installed alongside \u003ca href=\"\/collections\/fire-burglar-alarms\"\u003efire and burglar alarm systems\u003c\/a\u003e or \u003ca href=\"\/collections\/access-control\"\u003eaccess control systems\u003c\/a\u003e. 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 recessed reed contacts, rolling shutter contacts, wireless Tuya door sensors, alarm panels, sirens, relay modules, and cabling. Tell us your door type and what you are connecting to, and we will specify the whole installation rather than just the sensor.\u003c\/p\u003e","brand":"ZZ Marts","offers":[{"title":"NC","offer_id":52827954708792,"sku":"DH-55 NC","price":1499.0,"currency_code":"PKR","in_stock":true},{"title":"3 WIRE (NO\/NC)","offer_id":52827954741560,"sku":"DH-55 NO\/NC","price":1999.0,"currency_code":"PKR","in_stock":true},{"title":"With L bracket","offer_id":52827954774328,"sku":"dh-55 L Bracket","price":2299.0,"currency_code":"PKR","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1012\/3932\/4984\/files\/ChatGPT-Image-Dec-20-2025-06_16_47-PM-1.png?v=1787211128","url":"https:\/\/zzmarts.com\/products\/door-magnetic-sensor-102-aluminium","provider":"ZZ Marts | Zam Zam Traders","version":"1.0","type":"link"}