The law explicitly prohibits the use of devices to actively block mobile phone signals, but there is no rule prohibiting mobile phone passive shielding. For example, this means using wallpaper or building materials with embedded metal pieces to prevent cell phone signals from entering the room or out of the room. Some buildings are designed to accidentally block radio signals due to thick concrete walls and steel frameworks.
The company is working on devices that control mobile phones but do not "interfere" with signals. The device sends the incoming call to voice mail and blocks the outgoing call. The argument is that the phone is still working, so it won't get technically stuck.
Mobile phone alerts can be used to indicate the presence of a mobile phone signal. These are used in hospitals and cell phone blocker can interfere with sensitive medical devices. When a signal is detected, the user will be prompted to turn off the phone.
To reduce the technical content, Chicago-based design company Coudal Partners has founded SHHH, a Handushed Hushing Association. On the website, you can download notes that can be forwarded to people who interfere with the call and express that you are not interested in the content being discussed.