I have an old cottage with a boat hoist at the end of a dock. The electrical power to the dock and hoist is controlled by a switch in the house. Sometimes this switch is forgotten when taking the boat out, or is mistakenly turned off by someone who stayed behind while the boat is out making it impossible to lift the boat upon return. Rough waves from passing cargo ships can beat my boat to pieces in the slip if I don't lift it in time. Since cell service is not so great where we are what I would like to do is to place a phone (in a weather proof box of course) at the dock and another in the house. Essentially making a sort of Ringdown phone. I have found diagrams where this is done with a 9v battery; however, since my experience in the Marines has proven that batteries are always dead when you need them most and the house current is never shut off I'd like to wire in power there which both phones would operate from. Also these diagrams I've found don't allow for any kind of ringer or buzzer, that is imperative to get someone's attention ideally by just picking up the handset and the ringing or buzzing ceases when both are "off hook". The house and hoist are a little less than about 200 feet apart. Cutting, crimping, and soldering I can do; it's not blowing it all up or starting a fire where I have problems; Marine.
Side note: The house has an existing phone line left over from when it was a year-round house which is not used anymore; it's still hooked up but can't make or receive calls. Could I just patch in an extension and run the line to the dock? Would that be easier? How would I make the phone ring?