Crowded rooms can slow down your Wi-Fi because human bodies absorb the signal.

Wi-Fi routers typically transmit data using radio frequencies of 2.4 GHz or 5 GHz. These specific frequencies are part of the microwave spectrum, which is the same range used by microwave ovens to heat food. Because water molecules are polar, they rotate and vibrate when exposed to these electromagnetic waves, effectively absorbing the energy.The human body is composed of approximately 60% to 70% water, making it a highly effective attenuator of Wi-Fi signals. When a signal hits a person, some of the energy is reflected, but a significant portion is absorbed and turned into a tiny amount of heat. This phenomenon is known as signal attenuation, and it can lead to dropped packets or slower connection speeds in dense environments.Research conducted by institutions like the University of California, Santa Barbara, has even shown that Wi-Fi signal fluctuations can be used to count the number of people in a room. By measuring how much the signal drops as it passes through a space, researchers can estimate crowd density with high accuracy. This proves that every person added to a room provides an additional layer of resistance for the radio waves to penetrate.In large venues like stadiums or conference halls, engineers must account for this 'human interference' by placing routers high above the crowd. They often use directional antennas to focus the signal and compensate for the absorption caused by thousands of water-filled bodies. Without these adjustments, a full room could reduce signal strength by as much as 10 to 20 decibels.