That's okay, I've already got a CO checker for my scuba gasses. This one is for the hotel room. Thanks for the explanation of what they meant. Seems odd that the manufacturer's website omits this detail.Intrinsically safe means they are designed for hazardous locations and will not provide an ignition source for explosive gases etc. The other unit you show does not provide the sensitivity required for scuba gases.
I don't know how specific that word actually is. To answer your question, the Sensorcon units give fast results to low concentrations, while the First Alert unit requires much higher and/or longer concentrations before the alarm is sounded - yet still will give adequate protection. It's all relative. 1,000 ppm CO is quickly a threat, while 100 ppm is a low level threat at ambient levels, unless you compress it to breathe at depth where 10 ppm is the maximum allowed in the US.
Thanks!