If it is not possible to check the sticker with the IDentifier code at the back of the IDentifier (for example because it is mounted on the wall) you can also do this with a Podcatcher.
To do this take the following steps;
While the Podcatcher is still in the docking station > press the two left buttons (A/B) with both thumbs and take the Podcatcher out of the docking station while pressing. Wait until all the lights are blinking and then release the buttons. Now aim the Podcatcher at the IDentifier(s) and the Podcather will tell you the serial number. (Note on the interior of the IDentifier there is also a sticker with the IDentifier number programmed)