life alert is that thing the little old lady has in the "i've fallen and i can't get up!" commercials. i was being sarcastic
you are right that they are serious hazards. the best things for the trees or other potentially hazardous situations (avy terrain) is to always ride with a partner and to use good judgment.
an avalung simply was not designed for this purpose. would it give you extra time in some treewell situations? sure, yes.
in an avalanche you have 15 minutes of air without the help of an avalung. the snow of an avalanche is much denser (think concrete) then the snow of any treewell that you could sink into, so... see how its an apples to avocados kinda thing? yes you could breath longer with an avalung in your mouth when you went into a treewell, but rarely will you be chilling out for 20+ minutes unless you're unconscious or really really stuck.
you'd be better off with a cell phone.
get the hell off my lawn.