Supposedly there's a way to build without it. It's called normal and with it it's called sdk. However that seems to be too much trouble. There was also a way to have a trigger when the devtools were opened so it could then be closed immediately, unfortunately this was depreciated in newer nw.js versions.
The best we can do is disable the shortcut keys to open the devtools. Use the browser object to run this js at the start of the layout.
"document.onkeydown=function(e){var evtobj = window.event? event : e;if (evtobj.keyCode==123 || (evtobj.metaKey && evtobj.altKey && evtobj.keyCode==73))return false;};"
I got it from this link, and it's supposed to work on windows, linux and mac.
http://stackoverflow.com/questions/3365 ... on-nwjs-13