2004 Nissan Micra intermittant remote locking

All of a sudden the remote locking on my daughters Micra only works when i hold the keyfob right by the passenger door mirror happens with both keys. I read that the signal can be interrupted by some Wi Fi networks or radio signals. I fitted a Fluxscore black box to the windscreen last week in the bottom left hand corner but the problem only occured yesterday any ideas please...