A sizeable chunk of Shenzhen's prosperity can be traced to this vast cottage industry of tech that stretches across city blocks. Mall after mall selling every tiny electrical component imaginable has helped make Shenzhen the world's tech manufacturing hub. It's fascinating to browse around, and you'll also find stores selling all manner of cheap, 'made in Shenzhen' gadgets and gizmos.
A word of warning: avoid the temptation to buy Chinese Android smartphones. Government regulations restrict the installation of the Google suite of apps (including Play Store), effectively crippling them for non-Chinese users.