The debate between whether to use a mechanical combination lock vs an electronic safe lock seems to be rife with claims with little evidence to back them up.

The pro-combination lock folks are erring on the side of caution to ensure that you have access to your safe contents when you need it the most.

The pro electronic lock folks say worrying about an EMP is moot because:

  1. The e-lock is floating and not tied to the grid (they generally run off of two 9V batteries)
  2. The actual locking mechanism which stores the combination in a PROM is behind the steel plate door of the safe which would act as a Faraday cage. Only the keypad is exposed on the exterior of the safe.
  3. The required magnitude of an EMP to take out an e-lock is so large that your body would quickly succumb to the radiation exposure.

So, are the pro e-lock folks right? What would it take to take out an e-lock and would I be around to even see it?


closed as primarily opinion-based by placeholder, Anindo Ghosh, user36129, Dave Tweed, PeterJ Nov 10 '13 at 23:08

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ if there is little evidence then it boils down to speculation and who can possibly say what the truth is \$\endgroup\$ – Andy aka Nov 10 '13 at 9:57
  • \$\begingroup\$ A faraday cage is not some magical device that blocks every and all magnetic fields - it is an attenuator that uses the fact that ferromagnetic materials have a very high magnetic permeability to attenuate a magnetic field. However, these materials have frequency and saturation properties that can certainly be abused to still 'zap' an electronic device behind there. The myth of Ocean's Eleven's truck outside a building generating enough magnetic field strength is of course bullshit, but a small handheld EMP generator next to an E-lock: certainly possible. \$\endgroup\$ – user36129 Nov 10 '13 at 10:54
  • \$\begingroup\$ Very little probability of either failing, but they can. In any event the manufacture can gain access using their knowledge of the lock/door construction. A keypad may melt in case of a fire, and fire protection is really what a safe is designed for. \$\endgroup\$ – Optionparty Nov 10 '13 at 14:08

Some EMP tests carried out in 1986 suggest that small electronic devices (even sensitive ones) that are not connected to long wires (power, network, large aerials) should survive an EMP.

enter image description here

This suggests that a battery powered circuit inside a thick steel box would be relatively safe.

  • \$\begingroup\$ Follow-up question. Taking into account that electronics have changed considerably in the last 30 years since this test, how relevant are these results today? Trace lengths have definitely become shorter which would add to the robustness against an EMP but also ESD sensitivity and voltages have dropped considerably which makes me think a latch-up type failure would be easier to obtain. Your thoughts? \$\endgroup\$ – SiegeX Nov 11 '13 at 0:03

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