Angel care sensor pad is just a piezoelectric disk and a couple of plastic plates. The real Angel Care box probably does DSP to pick out heartbeat or at least

Angel care sensor pad is just a piezoelectric disk and a couple of plastic plates. The real Angel Care box probably does DSP to pick out heartbeat or at least breaths, so it can raise the (frequently false) alarm if something goes wrong, presumably to trigger parent action that's fast enough to prevent a SIDS death. That's the theory anyway. In practice the false alarm rate is too high. The algorithm I do use: Over a configurable number of samples, find maximum and minimum reading. Add the difference to an accumulator. Repeat. Once a minute, retrieve the accumulator and reset to zero. With 1-minute binning, it would be too slow to raise a "not breathing" alarm - but it's perfectly fine for post-analysis. I've used it for years, and can tell with a glance at the graph how bad the night was.