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.