Thanks–most Home automation manufacturers call those “contact sensors” if they are based on a two piece device with a magnet in one piece and a reed sensor on the other. Some call them “door/window” sensors.
These aren’t WiFi, but the Cao Gadgets Kumo Wireless tags have a contact sensor (they call theirs a “reed sensor”) with excellent range and two ways of integrating with SmartThings. The sensor itself is $39. You will also need the $39 Ethernet bridge (one bridge for each 40 sensors).
They have their own IFTTT channel, so you can get integration that way, or there is a community created cloud to cloud integration.
Manufacturer site:
IFTTT channel:
SmartThings integration:
Other options
You can build your own WiFi sensor for about $10 and connect it through IFTTT
Monnit has a WiFi door sensor for about $60, but to get integration you have to also buy their professional monitoring option so that you can send an email to IFT TT. A couple of years ago, that was a good option, but now I think you’re better off with either the wireless tag or even building your own.
DLink had a nice WiFi motion sensor with an ifttt channel, but no contact sensor.