Gas detector in industrial refrigeration processes and biological degradation processes, including exhaled breath. Depending on the required sensitivity, different types of sensors are used (e.g., flame ionization detector, semiconductor, electrochemical, photonic membranes). Detectors usually operate near the lower exposure limit of 25ppm; however, ammonia detection for industrial safety requires continuous monitoring above the fatal exposure limit of 0.1%. There are several different sensors that can be installed to detect hazardous gases in a residence. Carbon monoxide is a very dangerous, but odorless, colorless gas, making it difficult for humans to detect. Carbon monoxide detectors can be purchased for around US$20–60. Many local
Lawn mower are still available. The reel is attached to the mower's wheels by gears, so that when the mower is pushed forward, the reel spins several times faster than the plastic or rubber-tired wheels turn. These types of reel mowers offer the benefit of zero pollution being produced. Since all of the energy necessary comes from the user, however, this method of mowing is the most strenuous and is not recommended for large lawns. Depending on the placement of the reel, these mowers often cannot cut grass very close to lawn obstacles, like trees, driveways, edging, etc., and also require a