I came across an interesting article on  Thermochromic tapestry changes color in response to Wi-Fi signalswritten by Ali Morris
Below the short extract:

(…)”The thermal elements embedded in the tapestry then convert the current to heat, which causes the thermochromic yarns to change color.”(…) 

(…)”Wi-Fi Tapestry is a dynamic wall hanging that visualizes the wireless activity of a space. The tapestry visualizes the ever-changing landscape of radio frequencies around us.”(…)