I see people looking for some easy means of monitoring whether a device is on or off. If there appears to be enough demand for something like that, I am thinking about offering one.
About three years ago
glt posted about a similar device. I am not sure his links still work.. or that his post is overly clear.
Since his microwave would mess up his audio receiver and cause loud static. He used a special coil and circuit to determine if power was being used by his microwave. When the microwave would draw enough power (drawing more than the clock) the device would turn OFF the audio receiver while the microwave was ON.
A pre-made device like this... may have some marketable uses... for determinding if manually controlled/operated devices are being used. But, I think what many users want/need is a way to know if a X10 device (light switch) has been manually turned on. Which as we know... can be done with different switches... instead of the cheapie X10 ones.
What might be handy is a software that allows the HA PC to remember the status of ALL house/unit codes. But... didn't
bitman just post that. But combining the two... could allow a user to know how often or how much time his furnace is running while away. Or how late a teen is watching a TV.
Or
even to get an email notice if the sump pump kicks ON... Are you considering a plug-in type device? That would sound good to me.