46 CFR §27.201

1. (a)You must ensure that your vessel is fitted with a general alarm that:
   1. (1)Has a contact-maker at the operating station that can notify persons on board in the event of an emergency.
   2. (2)Is capable of notifying persons in any accommodation, work space, and the engine room.
   3. (3)Has installed, in the engine room and any other area where background noise makes a general alarm hard to hear, a supplemental flashing red light that is identified with a sign that reads:
   4. (4)Is tested at least once each week.
2. (b)You or the operator may use a public-address (PA) system or other means of alerting all persons on your towing vessel instead of a general alarm, if the system—
   1. (1)Is capable of notifying persons in any accommodation, work space, and the engine room;
   2. (2)Is tested at least once each week;
   3. (3)Can be activated from the operating station; and
   4. (4)Complies with paragraph (a)(3) of this section.