Re alarms, yes and no depending on what app you use with it and whether you're willing to use android.
The maker's inhouse app Linkblucon (there's both android and iPhone versions) isn't much cop: they keep on making noises about developing it to have alerts but are extremely vague - recent tweets and facebook stuff mention "voice notifications" and "target ranges" which suggest they might have introduced them, but even if they have, it's an extremely basic app and I've never really bothered using it.
But if you use the blucon transmitter with the app xDrip+ that definitely has alarms. However, it does not run on iPhone so that might be a dealbreaker for you. Many dexcom users use it in preference to the official dexcom app. It has pedigree.
Not trying to sway you one way or another - dexcom and libre/blucon/xdrip+ are both good systems which will wake you if you're getting near a hypo - but for me, it just boiled down to the cost. I just wasn't that keen on the startup costs of dexcom, the ongoing costs of buying replacement transmitters, and the fact that sensor restarts don't always extend life to 2 to 4 weeks: some people only get 10 days. With libre, I knew it would be a definite £100 per month (now £70 - there's a chemist near me selling at NHS cost price of £35) and then adding the blucon transmitter was £100, I expect that to last well longer than a year - it's just a bit of electronics with a cheap replaceable CR2032 battery - and xdrip+ was free.
I started a thread at link below about blucon which gives some details if you're interested in following that route. A caveat is that the makers are a small start up company, seem to have been overwhelmed by demand, their ordering system is shambolic, and people have experienced delivery delays - for all I know, it might go out of business, always a risk with small startups. Dexcom is definitely the safer option as a large well established company, but that brings you back to the higher costs of replacement transmitters and hoping sensor restarts extend it to more than 2 weeks. In fairness, most people have no problems restarting.
Whichever route you take, have fun! Full cgm really does level the playing field.
https://www.diabetes.co.uk/forum/threads/getting-hypo-alerts-with-libre-blucon-and-xdrip.127195/
