Connection type= SPST (Normally close Connection).
Physical Size= 20mm length, 2.5mm dia
The reed switch is an electrical switch operated by an applied magnetic field. Reed Switch Sensor Reed Sensor Magneto Magnet Magnetic Switch.

This is a small device called a reed switch. When the device is exposed to a magnetic field, the two ferrous materials inside the switch pull together and the switch closes. When the magnetic field is removed, the reeds separate and the switch opens. This makes for a great non-contact switch. This switch can carry up to 1.2A.

If you’ve got a laptop computer or a cellphone that flips open like a clamshell, you’ve probably noticed that it senses when you open and close it and switches on or off accordingly. But how does it know some kind of switch wired to the hinge so it can detect the opening and closing movement If that’s what you think, you’re at least half right! Think about it more carefully and you’ll see a standard switch would be quite tricky to wire up in that way—and probably quite unreliable too: all that opening and closing would quickly wear it out. So, instead, many laptops and phones use an inexpensive and very reliable device called a reed switch that turns on or off when a magnet is nearby. Intruder alarms and model railroads often use them too. Let’s take a closer look at how they work!

Reed switches come in two main varieties called normally open (normally switched off) and normally closed (normally switched on). The key to understanding how they work is to realize that they don’t just work as an electrical bridge but as a magnetic one as well: magnetism flows through them as well as electricity.