A distinctive row of lights runs across the bottom of this otherwise unassuming clock. They are part of a system of lights and bells that summon Members to the House Chamber when their presence is required. Signal lights and bells were introduced in the 1890s, and became essential when the Congress constructed office buildings soon thereafter. The system was modernized many times over, and this clock along with it. While the original case is generations old, its works were replaced with a series of increasingly tangled wires, connections, and motherboards that linked it to the House Floor.