I had to do a small site audit recently, a mixture of DrayTek routers, Netgear Draytek and Cisco switches.
The only products I couldn't get serial numbers for (through a GUI) were the DrayTeks.

True. You can get the MAC addres, which is specific to the unit.

Just seems a shame because the serial number is obviously "exposed" somewhere - registering a unit through the Product Registration button manages to find the serial number

The s/n is not stored in the unit.

Ah thanks for that - saves me digging any further (into the unit) then

That's would help as can't get draytek support as all my draytek units are in racks , removing to get serial number would take ages, ( 5 x draytek 2860's & 4 x Vigor130's ) plus all AP 900/902 are mounted in ceilings etc

If I get a issue that could be sorted via draytek U.K. Support I can't get serial numbers for the support form