Some Oregon models can take up to 5 sensors.

The 5 channel sensors can be used on any channel.  The 3 channel sensors can only be used on channels 1, 2 and 3.

For example, if you have:

• two 3 channel sensors and one 5 channel sensor you have 'space' for a third 3 channel sensor and one 5 channel OR two 5 channel sensors. 
  
• three 3 channel sensors and one 5 channel sensor, the only sensor you can add is another 5 channel sensor.