Database Model for Various Type of Sensors
Depending on how you plan on using the reading values, I would lean towards option 2 for this. Since you have different categories of sensors, with different types of values being used for each, then it would make sense to to have a master table that stores all the sensors and their type and status (online/offline) and location. There would then be a table for each of the types. This would make it easier to process the data over time, such as average temperature over time. 

If you just want to store the data without much processing, then going the one-table route would be best, and store the values as VARCHARs. This would make adding a type later on easier, but would make manipulating the data in the future more difficult.