Officially, it stores 8 hours of data in five minute intervals and you have to read it with an NFC device, so automatic alarms are a no-go.
If you want to hack, it is possible to turn the Libre to have automatic alerts. I did it, it's not perfect, but if you have nightly hypos which you don't notice, this can be helpful:
If you want to hack, it is possible to turn the Libre to have automatic alerts. I did it, it's not perfect, but if you have nightly hypos which you don't notice, this can be helpful:
https://github.com/pimpimmi/LibreAlarm/wiki
http://www.freestylesticker.com/product/freestyle-libre-cgm-...
If you're in Europe, I have one modded Sony Smartwatch 3 which I can sell :)