🪷ওমর🌸 on Instagram: "Before modern electronics, safety relied on clever physics and design🧠🪫 In the 1930s, engineers introduced mercury-filled phase failure relays to protect lifts and escalators from electrical faults. These devices were designed to detect a loss or imbalance in power supply, which could cause motors to overheat, stall, or operate dangerously. When a phase failed, the mercury inside the relay would shift, completing—or breaking—a circuit to immediately stop the machinery, p