Safety Knights

Do you want it for emissions testing (for the sake of maintenance)? Or for occupational health (for monitoring employee CO exposure)?

If you want it for occupational health purposes, forklifts do not typically stay in one area long enough to set off a CO alarm like you'd have in your house. Those typically take several minutes of continuously high levels (often >100 ppm, sometimes >200ppm), so they're not very effective at that.

If you're wanting it for maintenance purposes, you'd need an exhaust gas analyzer (similar to style they use to test vehicle emissions).

Either way, it's only a snapshot in time.