For those of you like me who have older homes with older wiring, you may have some outlets without a ground post. Most Z-wave plug-in modules have a ground post (Third prong) and so won’t work with old outlets that don’t have a ground to the anyway to add a ground wire.
I’ve in the past found “ground less” z-wave modules, but they are usually dimmers… not good to use those with devices like radios or small appliances.
A few months back I found Hawking Z-wave modules and just recently added four more to be setup (or will add 'em after I upgrade to Hub 2.0 next week). These work great in the ST environment… they are just on/off, so work well with small appliances, and only have two prongs, so work great with those older outlets.
Your millage may vary of course, but I’ve been happy with my modules so thought I’d pass along the info. I don’t work for hawking or have any connection with the seller on eBay other than that I’ve bought from them twice in the past.