To produce an iPad Mini 2, Apple reports that 96kg CO2e are used. Regarding the sensors, embodied carbon data for individual electronics components is even more difficult to find, though calculations for microcontrollers[1] suggest that a worst case is 0.083kg CO2e per chip. Considering one chip that integrates radio and micro-controller and a separate chip for the temperature sensor, we estimate just over 0.166kg CO2e for the electronic components. We also add 0.024kg CO2e for the battery[2], and 0.173kg CO2e for the case[3]. We could not find reliable estimates for the carbon cost of a PCB and solder, so to factor that we doubled the carbon cost of the sensor node. This gives 0.726kg CO2e for each sensor node, or 3.63kg CO2e for 5 nodes, and a total of 99.63kg CO2e when the manufacture of the iPad is added.

In terms of running cost, the selected iPad model consumes 2.80W while idle with the display on. As we could not find a reliable value for the active usage consumption, we doubled the idle consumption to 5.60W as a conservative estimate. Assuming this is left on for the entire day, it totals to 0.0705kg CO2e per day [4]. 
For the sensor nodes, we refer to the energy consumption of the WirelessThings XRF wireless data module, the same as we used in our prototype. The total current draw from the radio module is 23mA when active, and negligible when asleep. Assuming that the sensor transmits readings every 5 minutes, and takes about 2 seconds to do so, the battery should last for almost two months before needing replacing (depending on temperature, and other environmental conditions).

As such, the cost of constructing the hardware would be approximately 99.63kg COe, and the running cost would be 0.0705kg CO2e per day. 

[1] http://tinyurl.com/o25fts2
[2] 240mAh lithium battery running at 5V at 0.02kg per Wh, based on http://tinyurl.com/ntypjy7
[3] 50g ABS case at 3.46kg CO2e per kg, based on http://tinyurl.com/nqslyjj
[4] 0.5246kg CO2e per kWh unit for grid electricity, based on http://tinyurl.com/nspuq7u