The Fox-Peterson one of these devices had two separate thresholds.  
The Fox-Peterson one of these devices had two separate thresholds.  One of these devices with a dynamic limit consisted of expandable copper wire attached to a steel channel and was named for May and Oatway.  Walter Jaeger accidentally invented one of these devices after his tests on poison gases failed.  Every year on April Fools' Day, the Australian government releases a reminder about these devices.  Modern types of these devices include the (*) optical beam and photoelectric varieties.  A "split spectrum sensor" and an alternative to the problematic "wave to silence" feature were added to the second version of the Nest Protect, one of these devices.  Many of the ionization types of these devices induce a small charge in the chamber to emit americium dioxide.  For 10 points, name these devices which raise an alarm to prevent you from burning to death.
The Fox-Peterson one of these devices had two separate thresholds.  
smoke detectors [or fire detector or heat detector or smoke alarms or carbon monoxide detector]