Hi, sorry I'm late to the thread, hope you don't mind if I answer anyway.
I don't think I would bother, since it would mean weighing out the tar each time I dosed. I'm sure there are people out there who would be more diligent though. Technology facilitates these awesome innovations in how we track, maintain, and alter seemingly everything. There was a new app developed and posted on the opiates subreddit relatively recently, it's functionality is to increase the safety of iv addicts who shoot up alone, as they are particularly at risk of fatal overdose. I think how it works is you enter a friend's number, and after a set amount of time passes, if you haven't interrupted the command, the app automatically will contact your friend so that they can (hopefully) contact emergency services. Here's the thread talking about it, and this is the link to the app. Obviously designed with a different sort of function to your idea OP, but I thought it was a complementary concept. And it is so amazing to see ideas get actualized that further the ideology of harm reduction. I thought it was especially cool of the developers to make this app because, if I recall correctly, they aren't users themselves, they just wanna help the community.
IV drug users (like me) often face a lot of stigma, and I appreciate people who, although technically outsiders to the community, have the desire to help us instead of perpetuating a status quo which contributes to potentially preventable deaths. So I think you should totally pursue your ideas, if you choose to. :)
TL;DR: Fuck yeah, thanks for trying to figure out how we can help others cope more safely with their addiction!