I've got a Westclox Baby Ben glow in the dark wind-up alarm clock that I've had at least 50 years [1]. I don't think that there is anything I have owned longer. It still works fine, although sometimes it needs to be slapped a little to get it going if it hasn't been used for several years. I still use it as a backup whenever I need an alarm in circumstance where an alarm failure would lead to serious, hard to deal with consequences.
Westclox definitely used radium at one time in their Baby Ben clocks [2], but from what I read they stopped in the early to mid '60s. Mine was bought around the mid '60.
Mine only glows after exposure to bright light, suggesting it is using phosphorescence rather than radioluminescence, and so should be safe, but it would be nice to check.
Would a homemade cloud chamber [3] work?
[2] https://www.youtube.com/watch?v=wp6Ddcc4GAg
[3] https://www.sciencefriday.com/educational-resources/build-a-...
CMOS sensors can detect gamma particles. If you have an android phone there's an app that actually works (assuming you follow the calibration steps properly)[1]. Apparently Radium mostly emits alpha particles so I'm not sure how effective this would be.
If you are thinking about buying an actual geiger counter make sure to get one with a working probe assembly. A lot of surplus geiger counters are sold without the probe assembly with is the expensive part and the thing that wears out[2]. The probe assembly also needs to be properly calibrated.
[1]: https://play.google.com/store/apps/details?id=com.rdklein.ra...
[2]: https://www.amazon.com/Atomic-Adventures-Islands-Forgotten-I...