This has been asked a couple of times before so you can find some old threads in the forum but the answer is, no, there aren’t any built for this use case.
There is a brand new device that just came out about a month ago which is intended as a light switch cover to fit over an existing device and actually physically moves the switch. So you might be able to set that up to throw a switch which you attach to your nonnetworked Device. We should note that even in the best of times, though, the battery only lasts about two months and some people find they run through batteries in a couple of weeks. So I don’t know if that’s of any use to you, but the device does exist.
Another tiny battery-operated actuator option which I really like and use at my own house are the Naran Push microbots. This is a tiny robot finger from a Korean engineering company. It has its own Bluetooth to Wi-Fi bridge, the Naran Prota, and its own IFTTT service/channel.
People use these for a lot of retrofit projects, like when you have a fancy coffee maker that you really like but the automated you just need a button pushed to get it started. Or in my case, I have a small blender where I can’t physically push the start button so I stuck a microbot on that. These aren’t Zwave, but they work well, and battery life is typically at least six months and often more depending on how many pushes you send. The only problem is they are expensive. $49 for each microbot. But they do let you solve some use cases easily which are very hard to solve almost any other way. So if you create a project which can be operated with just a simple button push, you could network it this way.
But as far as something like the Fortrezz Mimolite relay which was battery powered that you could wire into an existing circuit, it doesn’t exist on the US frequency. Probably the short battery life just means there’s too much consumer dissatisfaction to make it a viable product.
@Radio_Star has pointed out in another thread that Popp is now making an electronic door strike actuator on the EU zwave frequency that can be battery powered. They are probably banking on the fact that most stores are only opened two or three times a day. But it also offers a mains powered option.
Anyway, for people in the EU, it might be worth looking at: