It turns out an "alerter" is required equipment[1]: on or after November 8, 1999 a working alerter or deadman control shall be provided in the cont

It turns out an "alerter" is required equipment[1]: on or after November 8, 1999 a working alerter or deadman control shall be provided in the controlling locomotive of each passenger train operating in other than cab signal[2], automatic train[3] control, or automatic train stop[4] territory. [1]: https://www.law.cornell.edu/cfr/text/49/238.237 https://www.law.cornell.edu/cfr/text/49/238.237 [2]: https://en.wikipedia.org/wiki/Cab_signalling#Cab_signalling_systems_in_the_United_States https://en.wikipedia.org/wiki/Cab_signalling#Cab_signalling_... [3]: https://en.wikipedia.org/wiki/Automatic_train_control#United_States https://en.wikipedia.org/wiki/Automatic_train_control#United... [4]: https://en.wikipedia.org/wiki/Automatic_train_stop#United_States https://en.wikipedia.org/wiki/Automatic_train_stop#United_St...