Detect User If It Is A Bot

When user signs up is there away to detect if user is a robot?

Just in case it slips through. Currently I use a robots.txt file

On my robots.txt

Code:

User-agent: *

Disallow /

And On my head area in view

Code:

<meta name="robots" content="noindex">

There's only one rule - please don't tell anyone to go and read the manual.  Sometimes the manual just SUCKS!