Hawk Technical Specifications can be found here

There is 1 x Digital Input on the Hawk baseboard, with the below spec

• Configurable pull up/pull down
• 0-40V DC input range
• On/Off thresholds
  • On >2V
  • Off <1 V
• Can be used for pulse counting (max 40Hz)

The Digital Input can be used to monitor a switching input (i.e. door open/closed, pump on/off), or configured for pulse counting. 

When used as a switching input, in order to avoid higher sleep current draw, the input should not be left in the range 0.3V → 3.V.

When used for pulse counting - there will be additional battery drain caused by the count, dependant on the speed of pulses - when compared to a device which is sleeping.