Olympus made the Trip 35 from 1967 to 1984 and sold something in the order of ten million of them. It is small, it is quiet, and it needs no battery. It is also the camera most often sold as working when it is not, and there is one reason for that.
How it works
The ring of small squares around the lens is a selenium cell. Light falls on it, the cell generates a current, and that current moves the meter. There is no battery anywhere in the camera because there does not need to be.
It has two shutter speeds: roughly 1/40 and 1/200. The camera picks between them and sets the aperture. Focus is by zone — four symbols on the lens barrel, from a head-and-shoulders to a mountain — so you estimate the distance rather than seeing it.
The Zuiko 40mm f/2.8 on the front is a better lens than the camera's size suggests.
The one thing to check
Selenium cells die. Not all of them, and not on a schedule, but a cell that has spent forty years in the sun loses its output, and a cell that has lost its output cannot drive the meter.
The test takes five seconds and needs no film. Set the lens to A. Point the camera at a bright window and press the shutter — it should fire. Now cover the lens with your hand and press again. A red flag should appear in the viewfinder and the shutter should refuse to fire.
If it fires in the dark, the meter is dead. The camera will still make exposures, but they will be wrong, and no amount of careful shooting will fix that. A dead-cell Trip is an object to look at, not a camera to use, and it should be priced and described as one.
What else
The lens barrel should turn smoothly through the zone symbols and stay where you put it. Light seals, as with any camera this age, are probably tar by now.
The shutter should sound crisp rather than sluggish. There are only two speeds, so a slow one is easy to hear once you know the fast one.
What it is good at
Being in a coat pocket. There is nothing to set, nothing to charge, and nothing to think about beyond how far away the thing is. That is the whole argument for it, and it is a good one.
What it is not good at: low light, moving subjects, and anything that needs precise focus. Two shutter speeds is two shutter speeds.
Every Trip 35 that passes through Unseend gets the dark test, the bright test, the barrel, the seals and the shutter, before it is listed. If the cell is tired we say so on the page, and we say it in the first line rather than the last.