The BeOS kernel actually has such functions:

int32 is_computer_on(void)

Returns 1 if the computer is on. If the computer isn’t on, the value returned by this function is undefined.

double is_computer_on_fire(void)

Returns the temperature of the motherboard if the computer is currently on fire. If the computer isn’t on fire, the function returns some other value.

Makeshifts last the longest.