Alarm were indicated to the operator by annunciator horns, and lights of different colours. The crew-alerting system (CAS) is used in place of the annunciator panel on older systems. An annunciator on the display indicates the current entry mode. The stall warning system is a voice annunciator that says "stall, stall". An aviation annunciator panel will have a test switch to check for burned out lamps. In 1870, Gray developed a needle annunciator for hotels and another for elevators.