Modern currency counters use sophisticated technology to spot fake notes. Here is how they work:

• Ultraviolet (UV): Authentic currency paper does not glow under UV light, but normal paper does. The UV sensor detects this difference.
• Magnetic (MG): Real notes have magnetic ink in specific areas. The MG sensor scans for these magnetic properties.
• Infrared (IR): IR sensors analyze the thickness and density of the paper.

If your machine is frequently accepting fake notes, it is time to recalibrate or replace the sensors.