Switching & protectionBench electronicsHand tools, works as-is
Reed switch
Also called magnetic switch, door contact.
Two ferromagnetic contacts in a glass tube that close when a magnet is near. Alarm sensors, laptop lids (sometimes a hall sensor instead), some float switches.
If you are new to this category
A switch opens or closes a circuit. Some switches are for your finger. Some open when they get too hot and stay open. Those do not reset. A relay is a switch that a small current turns on so it can control a larger current. Use the rating printed on the part.
Click it and listen. Then use a meter on continuity, which beeps when the contacts touch. Do not guess that a small switch can run a motor.
Common is the moving contact. NO means normally open: that leg connects only while you press. NC means normally closed: that leg is connected until you press. Click the button while the meter is on continuity and write down which beep matches which leg.
Strong neodymium magnets. Hard-drive magnets slam together hard enough to blood-blister skin and shatter into sharp chips. They also wipe media and bother pacemakers.
| What to look for | Usual figure |
|---|---|
| Glass | Fragile. Bend the leads, not the tube, and not close to the glass. |
| Current | Small. A reed is a signal, not a motor switch, unless it is a large one and stamped that way. |
Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.
What people actually use it for
- Door and window sense
- A hidden limit
- Pair with a hard-drive magnet and it will work from farther than you expect
Leave this one when
The glass is chipped. It will fail later, in the closed position, which is the dangerous one for an alarm.
Buying a new one is the better idea when
A hall switch, if you need to drive logic cleanly without contact bounce.
How to tell if this one still works
Beep, then bring a magnet in. Note the operate distance; it depends on the magnet more than the switch.
Tools you will want: Meter, A magnet.
Where people actually find it
0 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.
| From | Call | How many | How often | Where it sits |
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