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Ask HN: Ideas for an access monitor/counter for a bank saftey deposit box?

8 points by sigmaprimus ↗ HN
I recently aquired a safety deposit box at my local bank and would like to use it to store some items. After doing a few searches regarding the boxes, I found several accounts of unauthorized access occurring from bank employees.

I was wondering if anyone knows of or has ideas for a device that I could leave inside the box that would keep count on the number of times the box is opened.

It would have to be non resetting and reliable enough to not give false counts.

Ideally a low power device that could operate for months or years without the need to change the battery that would record a time/date stamp of each time it was opened and closed.

My only idea so far is some sort of light sensor tied to a data logger arduino setup with simple encryption but I am concerned the power consumption of an arduino may drain batteries too quickly even in sleep mode.

Thoughts?

11 comments

[ 5.3 ms ] story [ 46.9 ms ] thread
1cvmask
You should have bigger fears of the feds and police confiscating everything in it under civil forfeiture laws:

https://www.latimes.com/california/story/2021-09-19/fbi-seiz...

https://archive.md/bLH4W

sigmaprimus
That's so crazy, there seems to be a lot of scary government overreach in that story and people should be fired. I will be able to account for all them items I am planning on storing from recipts, transaction records etc. My main reason for using a box would be to protect the items from fire and flood loss and also to have a place for my Last Will and Testiment that I know my benificiaries will find. The problem is I live in a small town and don't particularly want the contents, regardless of value being known though the grapevine by snoops.

You do bring up a good point though, a blanket seizure of all the boxes is a possibility I should consider. It almost seems like guilt by association but having dealt with government entities in the past I know how obtuse they can be.

f0e4c2f7
I think ideally you would want something lower tech than that.

Maybe some kind of mechanical counter that increments up one click each time the lid is closed on it.

version_five
What about a photodiode (I think thats the name) - something that is high impedance when it's dark and conducts when its light, connected to a battery powered analog watch that you set to midnight?

It would give you total time open, and you could either reset it or just write down the time whenever you opened the box yourself.

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sircastor
On your logger idea, many microcontrollers have watchdog timers that can trigger a “wake up and do this” routine. You could have the controller wake up once every couple of seconds and check an LDR. Then go back to sleep. With well written code, you could easily get a year out of a coin-cell battery
brokenmachine
It doesn't even need to wake up over and over if you set up the LDR to trigger an interrupt to wake it up.

Just put it to sleep indefinitely, and set it to wake from a pin change interrupt.

You'd need an RTC as well so it can log the time though.

For example a STM32L031 uses 0.5uA in sleep mode.