I am wondering how wristlet devices can safely measure a person's heartbeat without risk of electric shock. It seems everywhere I read, the threat of static discharge would be far greater with an electronic wristband. Isn't the "shortest route to earth" always through a person's body in this situation? The wristband and its internal battery ultimately are only connected by a person's body to real earth ground.
In the event of static discharge, thousands of volts are likely applied over some resistance in the watch - what guarantees, extra safety checks, and calculations are done to make sure this resistance is correct i.e. there isn't a short that goes through a person? Am I correct that the short case would ultimately go through whatever skin-contact electrode (lower resistance than the packaging) was being used to pick up the heartbeat signal from the wrist? Would these risks be mitigated using a high-resistance/high-impedance recording electrode?
For example, if discharge voltage were 1000V and deadly current were 1mA, a design with a factor of safety of only 1 would use recording electrodes with a resistance of 1 MOhm to avert deadly discharge. Real life you'd probably use 100 MOhm for safety?