So you're flying off for that long awaited sailing/boating vacation. You want to take your comfortable personal inflatable PFD (Personal Flotation Device, also called a Lifejacket or Lifevest) with you. But will the airlines let you?
In short, you need to check on your airline's website for their policy on this. The FAA leaves the decision of whether the Co2 cartridges that go into a PFD are allowed on board up to each airline. Airlines have different policies, and... many airline employees don't know the policy. So don't just plan to ask the TSA agent, or the person at baggage claim... they may well not know the policy, so will likely say no.
So, go to the airline's website and find the policy. If they allow, print out the policy, highlight the relevant text, and put it with your PFD in your checked luggage only. That way, it makes it easy for any airline employee or TSA person going through your bag to know it's OK.
Here's an example, link to the Alaska Airline's policy: