A dog? No but there are dogs that detect hypos, not sure about night times.
Well in April (rumours on release) Libre 2 is getting released which will have the ability to use blue tooth and work as an alarm.
Up until,then there is MiaoMiao or Bluecon both of which are blue tooth transmitters that connect to the Libre sensor and with either xDrip, Glimp on Android or Spike with IOS they will give you the ability to have alarms set to trigger for either hypos or hypers.