you can have 2 (maybe 3) temps if you want.
It is a small 3 wire thing that plugs into the nomadio receiver. Then you can ziip tie/ glue the temp sensor on to the item you want to monitor.
In the radio you can set min or maximum temps that you want it to sound off/vibrate an alarm telling you it has reached a certain temp.
So you could monitor your ESC, and you motor if you had 2 temps sensors.
The sensor uses 4 AA batteries. and it lasts a long time. If I use energizers, it will last days (the biggest power consumer for the sensor is the back light screen display, which you can set how long it stays on for)
The react uses a battery pack, I have read that the stock pack does not last a long time. Some have converted it to a AA system with a radio shack AA harness. Or amain hobbies sells better packs for the react. Maybe the react owners can comment on their battery life.
One thing to caution is that about 2 years ago nomadio pulled out of the RC market, and shifted their focus to military contracts. I know for a fact they are still doing customer support. But that is why alot of places are sold out of stuff. Nomadio also used to do a lot of adverting on RC universe forums, and support on their own forums. But they dont do that anymore. If you have customer support issue, E-mail them and they will get back to you. (3 weeks ago I had to send in a receiver that was not binding, and they replaced it.)
It can be hard to get V2 receivers. All though nomadio said they recently had a batch of receivers made, and amainhobbies will have most of them in stock.
Read through their forums for more info:
http://support.nomadio.net/