No. Ben Best has been trying to build a device like this for years (link from downthread); people very often say to him that it should be easy, but he never sees a finished prototype.

You know, in telemetry units in hospitals, most of the time a flatline means a lead came off, or something is unplugged. Lots of false positives could be an issue.

I'm not sure this is actually helpful. If the cryonics team isn't anywhere nearby having this information may very well translate close to "well, we're not getting that one." It would help but probably only in marginal cases. Still, could be potentially quite useful. There have been cases where a team has been on standby due to someone's ill health or is getting ready to go on standby and the person dies slightly earlier than expected. My impression is that in those cases they've generally still managed to preserve the patients fairly quickly. But we don't know how quick it needs to be. This could be the sort of thing where even small amounts of time could matter.

Currently? No.