@tehmilcho well, i dont have experience with a firetv but i would like to give a suggestion but i need more info.
Firetv is a android based system, right?
Can you access the terminal, a.k.a ADB?
If so, it shouldnt be a problem to cURL post a variable when it goes into sleepmode…
You can then act on this variable.
Yes its a Android modified by Amazon (without google store etc)
Im not so skilled in android …do you mine this?