CO is a toxic gas that can lead to death when critical levels are reached. The Health and Safety Authority limits for CO exposure are just 20 and 100ppm. Safe monitoring is achieved with our low cost handheld Carbon Monoxide monitor, the Crowcon Clip CO. Reliable and durable fixed life monitoring in a compact and maintenance-free package, the Crowcon Clip has a 2-year life. No service or calibration required. CO handheld portable gas detector. Our CO gas meter alarms at recognised dangerous levels to protect you from toxic gas exposure.