If anyone's trying to order one of these Frient heat alarms, a smart home supplier called Vesternet out of the UK seems to ship to the USA. I placed an order through German based smart home supplier, Reichelt, but they cancelled the order since the heat alarm has batteries inside and is deemed hazardous to ship.
Both companies are listed on the Frient site as distributors. I'll update this post if I run into issues with Vesternet.
