Red stars show sensors that are hidden under a cable or another component and the blue dots show sensors directly visible when the bottom plate is removed. Until now, only a few models of 17" MacBook Pro and MacBook Air had 8 of those sensors, the control level is now going up with 10.
Apple has used these sensors to refuse warranty service in the past. Recently the company revised its policy on repairs of iPods with activated sensors after numerous complaints that they were falsely activated.
If a customer disputes whether an iPod with an activated LCI has been damaged by liquid contact and there are no external signs of damage from corrosion, then the iPod may still be eligible for warranty service
Take a look at the image below to see where the sensors are located.