Hi, Everyone! I came across this little three terminal tube-like device. Is it an early flasher, or electronic fuse? The top of the metal can move out about .125". I'm not sure what, exactly it came from, it just turned up in one of my junk boxes!
Thanks!

 

Vibration sensor, tilt switch?

 

There is a "switch" from left to center pins. That I can see clear.
I cannot see enough. The right to center might be a heating element. It takes time to heat up the element so it opens up the contact in the switch. (flasher or time delay switch)
It also might be a tilt switch. Maybe the metal end that points down moves and opens/closes the switch.

 

Try testing continuity with the device in different positions.

 

Send more pictures. Show the other side. How much does the silver pieces move?

 

In the end is clearly seen the Hollow Cathode. Means neon lamp. But the third electrode means the gate what regulates voltage at which it ignites. Such russian devices are named Thyratron

 

Thyratron

Most Thyratron have a hot filament and many leads.
There are cold cathode Thyratrons. MTX-90 This one glows Neon red and is used as an indicator.

 

So, You referred to a russian MTX-90, exactly what I meant.

 

Is the metal slug in the end magnetic?
It looks like a reed switch with No and NC contacts.

 

I don't know, a mystery device walked into your box to hybernat?

 

I do not think it is a Thyratron. There are contacts. It is a switch. Do not know if it is a tilt switch or a magnetic switch. Both of which only need two leads. I think it has a heating element that caused a delay. (blinker maybe)

A picture from the other side will give more information.