Philips PSE0400 Operator's Manual page 18

charger (5V/0.5A or above) to energize the PSE-0400; use the
attached special charger to energize and start the PSE-0500;
② Pairing: Hold down the "U" key of the PSE-0400; pairing is
successful when the indicator on the PSE-0500 is constantly
illuminated other than flashing. In case of wireless connection,
one PSE-0500 supports up to four PSE-0400s, and pairing is
conducted from the 1st to the 4th, which means that the first
PSE-0400 is paired with the first position of the PSE-0500, so
on and so forth.
18 EN