We will need an HCN sensor that is calibrated within the last 30 days using a known calibration source. In the case of HCN, the best calibration is done by a certified agency with a canister of registered HCN gas. We selected the Industrial Scientific T-82 sensor as it is a higher resolution sensor (0.1ppm) as well as a leading brand used by firefighters as well as industry and chemical engineers worldwide. We requested certified calibration documentation along with quick instruction as to capabilities. The unit is more expensive than most single gas detectors but has a better rating than most.
Smoke and CO
Any standard smoke and CO detector as these are highly UL regulated and there are constant factory calibrations checks.