very non invasive, monitors just about anything and graphs via open libraries. opensource and pretty easy to get started.

My wife grew up in the UK. She and 5 other girls came over in 90 as foreign exchange students and they were concerned about coming to the DC area with the crime etc. They got to talking to an American soccer mom type and she said, "Oh, don't worry, you just need to get your self a fanny pack!" The British girls jaws all dropped. Fanny in the UK means vagina, so they were all envisioning a small (or large as the case may be) pack that you hide your valuables in and then insert into the holiest of holes for safe keeping. She saw their confusion and shouted to her husband (a few rows back), "honey, they want to see my fanny pack, pass it up here so they can see it!" The first exposure to English vs American, the "common" language that seperates us.