As Tursiops most accurately points out, it's absolutely critical for folks to understand that the new Nautilus Lifelines are
NOT a PLB and do
NOT communicate location coordinates to anyone via satellite. What the newer Nautilus Lifeline does do is broadcast your GPS position via a radio signal to all AIS equipped ships up to 34 miles (55 km) away as well as a DSC message to the designated marine radio on your own vessel. All modern commercial ships and most private boats are equipped with AIS and DSC. The statement "up to 34 miles" range should be taken with a grain of salt. That means perfect flat dead calm conditions communicating with vessels with the highest elevated antennas. My personal opinion is that 5 miles is a more realistic statement and expectation.
I have the older Lifeline that does all of the above...... plus it has the integrated Marine VHF radio that allows actual voice communication to my own boat and other boats within range, Coast Guard, etc....that are monitoring channel 16. For diving here in the PAC NW and mostly off of my own boat, the older Nautilus with VHF is a great option...... and I have never had any issues with flooding or function. There is an issue with British Columbia having licensing issues for any Marine VFH operations but I don't really care about that or worry about it. If I am in an emergency rescue scenario and the BC radio police want to come and arrest me for unauthorized Marine VHF radio use.........I'll be happy to see them!
I do also have a Global EPIRB on my boat that communicates via satellite and will basically send the Calvary anywhere in the world once activated ....but that's a whole nuther discussion and the unit is too large to practically carry on a dive and although waterproof with floatation, it is not designed to take diving pressures.
If you really want to have the absolute and best all all-around emergency location device then I'd say to go with an ACR PLB and contain it within an XL Dryfob which is sold by one of our great sponsors here on SB........ or other means of water and pressure proofing. Just my .02.
Here's pics of my "older model" Lifeline with VHS and also my primary EPIRB. Also a pic of my Large Dryfob that I use for my truck FOB and my XL Dryfob that accommodates an ACR PLB.