getting the personid of the current contact

Is there a better way to get the personId of the current contact than using getCgiVariable("personId")? Lately this has become unstable and often returns the personId of a previously viewed user.

The following script is run when a user clicks a button on either a contact card or a ticket/request. So what I need in the end is the x_personid, which is a custom field on person.

#setLanguageLevel 4;

Integer personId = getCgiVariable("personId").toInteger();

if (personId.isNull() == true || personId < 1)
{
  	setVariable("url",  getProgramBlogic() + "&action=doScript&includeId=close");
}

String externalPersonId;

SearchEngine se;
se.addField("person.x_personid");
se.addCriteria("person.person_id", "Equals", personId.toString());
if(se.select() > 0)
  externalPersonId = se.getField(0);

if(externalPersonId.toInteger()>0)
	setVariable("url", "https://bn.app.local/Customer/Link/" + externalPersonId);
else
  setVariable("url",  getProgramBlogic() + "&action=doScript&includeId=close");