I have this meta tag to check if JavaScript is enabled:
<meta http-equiv="refresh" content="0;url=http://www.example.com/activate_js.html">
Is this bad in the eyes of search engines like Google, Bing and Yahoo?
If so, what other “safe” methods are there?
META tag to check if JavaScript is enabled? Not sure I understand what you mean there…
With regard to the question about META tag redirects, these are bad for search engine optimisation (SEO). The correct way is to send an HTTP 301 Moved Permanently Header, either with Apache configuration or perhaps PHP.