This article explains how you can troubleshoot smart silence.
If your Smart Silence is not working this is usually caused by you changing the stimulation head.
Whenever you change the head on your Womanizer, Smart Silence™ feature must be recalibrated. To do this, the device must first be switched off. Remove the current head and then switch the device on. Smart Silence should now work, causing the LEDs to light up, but the device remains still and in stand-by. Now place the new head on the device and make sure that the head is inserted the right way. Now do not touch the head any longer and the device will automatically calibrate itself within the next 10 seconds. You can tell that it has worked successfully by the fact that the device will go back into stand-by and become still while the LEDs continue to light up. Your Womanizer is now ready for use as usual with Smart Silence.