How to detect when a lead is on my site?

How to detect when a lead is on my site?

Hi Guys, 

New here so be kind... :)

We are using Zoho CRM.
We currently have lots of leads / potentials within Zoho CRM.

I would like to be able to determine when an existing lead is visiting my site , and improve the lead score.
The visit may have initiated visit from an email campaign.

SalesIQ doesn't seem to be able to handle this as far as my trials have gone to date... 

Any help much appreciated :)