I have a metal cased device powered by 2x 1.5v AA batteries with a standby current draw of 19.7 microAmps. If I then cause a build up of static by shuffling across a synthetic floor and touch the metal casing, the current draw at least doubles to +50microAmps. I am unsure of the principles behind this effect.
What external factors (to the device) could cause increased current draw? Could an appliance in close proximity that charges capacitors to provide a burst of 10's of 1000's of volts which then discharges cause increased current draw?
Edit - 14:30 29/10/14 The board has a conformal coating and has passed EMC testing covering immunity for residential, commercial and light industrial environments.
65 identical devices were measured for current draw and all were consistently within a current draw range of 0.81uA.
Discharging a static charge by touching the metal casing cause a measurable increase in current draw. The larger the charge, the larger the current draw.
Measurement has been using a digital multimeter wired in series with the positive power feed.
Edit - 15:17 29/10/14 Some further information that has come to light - the device has a battery pack that is located within a metal cabinet (the device itself is on the outside of the cabinet). Also within the cabinet is a piece of electrical equipment that performs automatic self-tests. The battery pack has two wires running inside of the cabinet before going through a small hole to the external mounted device. From my research and suggestions below, it would appear that perhaps ESD or EOS is somehow in play. I do not pretend to understand this field and would appreciate any further answers regarding possible factors.