The "Shielding tester" application is designed to check the effectiveness of radio signal shielding in boxes, cases, bags, and other devices with radio signal blocking functionality. Here's how to use it.
Instructions:

1. The app checks cell signal (800 MHz, 900 MHz, 1800 MHz, 2100 MHz, and 2600 MHz), Wi-Fi (2.4 GHz, 5 GHz), and Bluetooth (2.4 GHz). To start, open the app. If your phone asks for permission, allow it.
2. Select the type of testing at the top of the screen. By default, the express test checks Wi-Fi or cell connection (depending on the current phone's internet connection). The full test checks Wi-Fi, cell, and Bluetooth.
3. Make sure your phone's sound is on, and volume is up. To test the effectiveness of shielding, slide the Start test slider.

For the Express test, put your phone in the shielding device right away.
For the Full test, wait for the connection types to show, then put your phone in.
When the test ends, you'll hear a sound. The maximum test duration is 150 seconds.

The results will show on screen:
If signals are blocked, it shows "Blocked" and a green checkmark.
If not, it shows "Test failed" and a red cross.
During the express test, the measurement continues until the signal is blocked.

Note
Starting from iOS 11 and higher, the calculation is made using a methodology that gives measurements with an error of ±5 dBm. For correct operation, the application requires all access rights requested at startup.
The obtained results are not accurate and are intended to provide an approximate representation of the signal level and shielding quality.
For more info or to buy shielding devices, visit velter.co