1 · Case: glass tube
The reed contacts are sealed inside a glass tube. [HSI · Reed Switch Basics]
Teaching view: The pale glass tube surrounds two metal reeds. The switch detects a nearby magnet; the tube view lets you locate the contacts inside.
IoTClass Inside the measurement
A closer look · 01Sensor
Look inside
a sensor.
Reed switch
A reed switch is a small switch that detects a magnet and gives an open or closed state.
In a normally open reed switch, two flexible ferromagnetic blades sit sealed in a glass tube with a small gap; a nearby magnet's field magnetises the blades so they attract and touch, closing the circuit; remove the magnet and the blades spring apart.
An IoT door or window monitor reads this open or closed state to tell whether the door or window is open.
Test the switch in its installed position across the expected operating range, because placement can affect whether it responds reliably.
01
Recognize the element
Recognize the element: Reed switch
02
Peel the teaching model
From case to sensing element
Choose a layer to see the measurement path. The enclosure and board layout are invented teaching choices, not a particular product.
The full text version below describes every layer. All measurement explanations are available without 3D.
Conceptual, not to scale
Case: glass tubeThe reed contacts are sealed inside a glass tube. [HSI · Reed Switch Basics]
Drag to rotate; pinch to zoom. With the view focused: arrow keys rotate, + / − zoom, 1–3 choose a layer, Home resets rotation and zoom. Step advances to the next layer; Reset returns to the case and default view. Layer buttons select a view directly. The page does not move on its own.
Layer 1 of 3 / Outside
Case: glass tube
The reed contacts are sealed inside a glass tube. [HSI · Reed Switch Basics]
Teaching view: The pale glass tube surrounds two metal reeds. The switch detects a nearby magnet; the tube view lets you locate the contacts inside.
The measurement to rememberA magnetic field can close the contacts of a normally open reed switch. [HSI · Reed Switch Basics]
Full text version · every layer
2 · Interface: two leads
This teaching view shows two leads extending from opposite ends of the switch, with no interface board. [HSI · Reed Switch Basics]
Teaching view: Two leads extend from opposite ends of the glass tube and connect to the reeds inside. These are the connection points shown for the switch.
3 · Element: two reed contacts
The contacts close when the magnetic force becomes stronger than the spring force holding the reeds apart. [HSI · Reed Switch Basics]
Teaching view: Two silver reeds overlap with a small gap between them. The gap shows the contacts apart; follow each reed outward to its lead.
Explore the layers in order to follow the teaching model.
03
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Package narration
Read transcript
Maya is fitting a connected greenhouse door monitor. She mounts a magnet on the door and a normally open reed switch on the frame, then checks whether opening the door changes the contact state.
Inside the switch, two flexible metal blades sit almost touching in a sealed glass tube. The blades are magnetic material. A nearby magnet gives their facing tips opposite magnetic poles, so they attract. When that attraction overcomes the blades' spring force, the tips touch and complete an electrical circuit. Moving the magnet away weakens the attraction; the blades spring apart and break the circuit. The controller reads that open or closed state to monitor the door.
Maya assumes a nearby magnet will close the switch however she mounts it. But the field must pass through the blades strongly enough: magnet alignment and the gap both affect when it closes. She tests the actual mounting while opening and closing the door, then adjusts the magnet position until the switching matches the door movement.
The takeaway: a reed switch senses a magnet, and tested placement turns that contact state into a useful door signal.
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