According to the user docs, they’re rebranded Linears (same as 2Gig, good catch). All zwave devices. Support is provided by Nortek–that’s Linear’s new more searchable name. The motion sensors are linear WADWAZ 1. I haven’t looked up the siren.
The Linears aren’t on the official “works with SmartThings” list, I’m not sure if there are any incompatibilities.
Individual price is typically around $50 each, although the siren is often thrown in as a freebie in a security kit with 3 of the others. Even so, $100 for 4 sensors and a siren is indeed a really good deal.
And here is more on Nortek’s very complicated branding strategy. Linear (now Nortek) is intended to be sold to pro installers, while GoControl will be sold at retail as a DIY brand, and 2Gig remains the monitored security offering. Elan is a separate brand for high end products. But many standard items like contact sensors are the same devices, just rebranded.