I'm weighing in at just 51.2 grams (with battery and sim, according to my scale). It's comparable to a flip phone, but about 2/3 the size, and half the weight. I bought a pre-paid, and stole the sim from it. I only pay on the days I use it.(unlimited texting ;-)) It texts me it's position every minute or so, depending on what text commands you send it.
Then you essentially send it a "stop" command. Some of the reviews on Amazon are negative, but that is from people who don't know how to use it. I experienced a small lag in position coordinates, maybe a minute or 2, just like receiving a text message. It is a great backup to total power failure, and will last 2 or 3 days on a full charge. The beacon also sounds like a great idea.