An electronic device such as a wristwatch may have a housing with metal sidewalls and a display having conductive display structures. Printed circuits having corresponding ground traces may be coupled to the display for conveying data to and/or from the display. The conductive display structures may be separated from the metal sidewalls by a gap. A conductive interconnect may be coupled to the metal sidewalls and may extend across the gap to the conductive display structures. The conductive interconnect may be coupled to the ground traces on the printed circuits and/or may be shorted or capacitively coupled to the conductive display structures. When configured in this way, the metal sidewalls, the conductive display structures, and the conductive interconnect may define the edges of a slot antenna resonating element for a slot antenna.