I bought a random cheap crystal oscillator off AliX. It was advertised as a "constant temperature crystal reference".

I also didn't know what voltage it took. I found a photo of a similar one which apparently needed 12 V. However, smoke started coming out when I tried 12 V.

It seems to oscillate OK on 5 V though. However, it seems to be fluctuating in frequency, and I don't know if this is normal, or whether I have damaged it.