Had a look at the pre-order page. Looks like there's two versions, Transam 35 dollars but only lasts two weeks, and Nightrider which is reusable for 110 dollars. The disposable one seems to be waterpoof, the reusable one isn't, but seeing as you need to hold the reusable one on with an armband, it's presumably easy enough to take off for showers.
Pricing seems a bit crazy, why pay 35 for something which only lasts two weeks when 110 lasts longer? The price per unit comes down the more you buy.
Can't see anything on the site itself about whether it alarms or not, but there's a recnt post on their twitter feed saying it alarms. If it does, I'll definitely think about getting one. Don't mind scanning but the idea of an alarm while sleeping is very attractive.