diff --git a/USB-protocol.md b/USB-protocol.md
index e6fb194..53a6b46 100644
--- a/USB-protocol.md
+++ b/USB-protocol.md
@@ -65,6 +65,8 @@ Device Status:     0x0000
   (Bus Powered)
 ```
 
+Note: the serial number matches the one on the sticker on the bottom of the plastic shell.
+
 ### Protocol
 
 The device operates in two (or three, depending on how you count) operting modes: bootloader mode (and authenticated bootloader mode), and application mode.