Small glass tubes containing three tiny ball bearings are most commonly one of the following:
1️⃣ Tilt / Vibration Switch (Most Likely)
These are often called ball tilt switches or mercury-free tilt switches.
What they do:
- Detect movement, tilt, or vibration.
- When the tube is tilted, the metal balls roll and complete (or break) an electrical circuit.
Where they’re used:
- Simple motion alarms
- LED novelty items (like flashing toys)
- Basic orientation sensors
- DIY electronics projects
They replaced older mercury tilt switches because they’re safer and non-toxic.
How to recognize it:
- Very small glass tube (often 5–15 mm long)
- Two wire leads coming out each end
- Loose metal balls inside
- Makes a faint rattling sound when shaken
2️⃣ Reed Switch (Less Likely if You See Loose Balls)
A reed switch is also in a small glass tube, but:
- It contains thin metal reeds, not loose balls.
- It activates using a magnet, not movement.
If you clearly see three loose ball bearings, it’s not a reed switch.
3️⃣ Time-Delay / Mechanical Sensor (Rare)
In some older devices, ball-in-tube assemblies were used as:
- Simple delay triggers
- Shock sensors
But these are far less common than tilt switches.
Quick Test (If You Have a Multimeter)
Set it to continuity mode:
- Hold the tube one way → no connection
- Tilt it → you should hear a beep
That confirms it’s a tilt switch.
If you’d like, you can describe:
- Approximate size
- Wire leads or not
- What device it came from
And I can narrow it down further.