SnO is used in sensors of combustible gases including carbon monoxide detectors. This limits their use in applications such as sensors, detectors and transducers. Ionization smoke detectors are usually cheaper to manufacture than optical detectors. Travelers are screened by metal detectors and/or millimeter wave scanners. It is also used in infrared detectors. InGaAs uses less hazardous wavelengths than conventional silicon detectors, which operate at visual wavelengths. In 1955 simple home "fire detectors" for homes were developed, detecting high temperatures. Some have also taken measures such as installing metal detectors or video surveillance. The bones were found using metal detectors and metal rods as probes. The table below provides information about laws regarding radar detectors in particular nations. Americium often enters landfills from discarded smoke detectors. Batteries are used either as sole or as backup power for residential smoke detectors. Americium-241 often enters landfills from discarded smoke detectors. Laws governing the installation of smoke detectors vary depending on the locality. It also has uses in neutron detectors.