cant understand people crowing on about the old grey boxes,used them week in week out , ferrets and terriers for 20 odd years and due to dampness went through two to three boxes/collars a season , bought a mk3 box and collar 6 years ago and still using it , got a magnetic collar last season and have to say its the job , batteries seem to last longer too ps dig to both ferrets and terriers with the mk3 been spot on everytime