Some of our models are provided with a HDD/SSD activity led at the front the HDDCaddy. This led will blink when your hard drive or SSD is being acccessed by your computer (reading or writing to disk). However support for this LED compatibility has become less with newer type of hard drives. Especially most SSD do not support LED activity read directly from the SATA port. In most cases your laptop already has a activity LED for reading drives, the input for this LED is different than the LED that is connected on the SATA converter board. Below is a picture of a Seagate and a Toshiba hard drive. The Seagate does not support LED activity for the HDDCaddy while the Toshiba allows the LED to blink whenever it is being accessed.