What to check

That the fob is compatible with the reader.  Entryphone fobs are laser etched each with a serial no. starting with PX or MX.  MX fobs are encrypted, where as PX fobs are not.  The fob reader will only respond if it is the correct type of fob.

Corrective action

Contact Entryphone to assess if you have the correct type of fob for that reader.