The Signal Level Indicator (SLI) shows the current strength of signal received, represented by four different levels of blue LEDs lighting up at the front of the antenna. A strong signal is represented by all blue LEDs lighting up; a weak signal is represented by one LED lighting up.
By moving the aerials direction and position, you can find the best reception in your room this way.
When plugging in the aerial for the first time to the power supply, the SLI will remain active for 30 seconds and then turn off. If you need to reposition the aerial, simply press the button on the front to reactive the SLI for another 30 seconds.