Summary: How to get the serial number of a Cisco device.
Date: Around 2010
Refactor: 21 February 2025: Checked links and formatting.

If you want/need support for your cisco devices you'll need the serial number. You can get it from the software, along with other interesting information about the device:

switch1#sh version
Cisco IOS Software, C3750 Software (C3750-IPBASE-M), Version 12.2(35)SE5, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Thu 19-Jul-07 19:15 by nachen
Image text-base: 0x00003000, data-base: 0x01080000

ROM: Bootstrap program is C3750 boot loader
BOOTLDR: C3750 Boot Loader (C3750-HBOOT-M) Version 12.2(25r)SEC, RELEASE SOFTWARE (fc4)

switch1 uptime is 2 years, 18 weeks, 5 days, 23 hours, 56 minutes
System returned to ROM by power-on
System restarted at 08:16:03 CET Thu Nov 27 2008
System image file is "flash:c3750-ipbase-mz.122-35.SE5/c3750-ipbase-mz.122-35.SE5.bin"

cisco WS-C3750G-24T (PowerPC405) processor (revision N0) with 118784K/12280K bytes of memory.
Processor board ID FDO1233Y2FK
Last reset from power-on
1 Virtual Ethernet interface
24 Gigabit Ethernet interfaces
The password-recovery mechanism is enabled.

512K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address       : 00:23:05:30:97:58
Motherboard assembly number     : 73-9679-13
Power supply part number        : 341-0048-53
Motherboard serial number       : FDO12660FDJ
Power supply serial number      : DTN1456309Z
Model revision number           : N0
Motherboard revision number     : A0
Model number                    : WS-C3750G-24T-S
System serial number            : FDO1456Y2FK
Top Assembly Part Number        : 800-25325-02
Top Assembly Revision Number    : A0
Version ID                      : V06
CLEI Code Number                : COMUV10ARA
Hardware Board Revision Number  : 0x02


Switch   Ports  Model              SW Version              SW Image
------   -----  -----              ----------              ----------
*    1   24     WS-C3750G-24T      12.2(35)SE5             C3750-IPBASE-M


Configuration register is 0xF