What is the technology for communication of esl labels and if they are bi-directional?

What is the technology for communication of esl labels and if they are bi-directional?

What is the technology for communication of esl labels and if they are bi-directional?
Sertag electronic shelf labels  uses radio frequency technology  2.4Gmhz ,but it is a private protocol. E ink price tgas  can feedback some key information, such as temperature, battery capacity, and signal strength etc.