Paras:
- sensor_name: str, the name of new sensor
- object_name: str, the name of the object sensor should watch
- rate: float between 0 and 1, the success rate sensor should has
- state: array, a list of physical conditions the sensor is watching
Return:
New sensor instance
sensor1 = myhome.add_sensor('c1_p_sensor', 'chair1', rate=0.8, states=['pressure'])