How to find that is Google updating?

Google never announce about updates.

updating

What Happen When Google Start updating its Database or algorithm. There are some observation to find out is Google updating.

Webmaster tool is not showing links/ or page will not load on click total number of links.
number of back links didn’t update since 10-15 in Google webmaster tool
Google spiders are slower than before. Will not crawled your web page since 10-15 days.
SERP (search engine ranking placement) result keeps changing.
Any of you link building efforts didn’t show up.