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Knowledge document #3696
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The display of the FRITZ!DECT smart switch is frozen

The display of the FRITZ!DECT smart switch, for example FRITZ!DECT 440, is frozen and shows old values. The smart switch no longer responds when you push a button and the connection to the FRITZ!Box is interrupted.

1 Checking the batteries

FRITZ!DECT smart switches have energy-saving e-ink displays, like the ones used in e-book readers. Such displays only require current flow when changing the display. If the batteries are removed, or if the batteries are dead or unsuitable, the last indication on the display continues to be shown.

Note:Refer to Wikipedia for more information on how an e-ink display works.

The error usually occurs when unsuitable or dead batteries are used. Proceed as follows:

  1. Remove the batteries from the FRITZ!DECT smart switch.
  2. Insert new batteries that are suitable:
    1. Do not use rechargeable batteries. Rechargeable batteries usually have a higher internal resistance and a higher self-discharge rate than disposable batteries and produce lower voltages. This can affect how the smart switch functions and shorten operating time.
    2. Do not use zinc-carbon batteries. Due to their construction, they are not suitable for use in smart switches.
    3. Use high-quality batteries. Varta Industrial Pro AAA, Varta Longlife Max Power AAA, GP Super Alkaline LR03, or Duracell Industrial AAA are suitable.
  3. Push the Menu button for about 2 seconds until the menu is displayed.
  4. In the menu, push the button labeled "Zurücksetzen".
  5. Reestablish the DECT connection to the FRITZ!Box.