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I have an object that I want to know whether it is submerged into water or not for a specific period(20 seconds for example). The object will float over the water most of the time but I want to be able to know when it is submerged into water. I don't want to detect water, I want to detect if it is submerged into water for some time...
What sensors can help me? I though to use Bluetooth: connect the object to another device that is outside the water, and as you know Bluetooth is not working underwater, so the both sides can knows that the object is now underwater and thus I can measure the period where Bluetooth was disconnected. What do you say about this way?

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  • \$\begingroup\$ I would like to post a quite serious answer to this for you, but I need you to come up with a quantifiable definition for 'submerged' and 'for some time'. To what depth? How long? And under what conditions is it insufficient? The problem with your problem is that you haven't yet completely defined what the successful design will accomplish. \$\endgroup\$
    – Sean Boddy
    Oct 12 '15 at 3:45
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One of the simplest ways to detect this would be to use a floating switch similar to the ones used in sump pumps in the US. Basically it consists of a float that has a density higher than air but lower than water that can move up and down a short post. When in air, the float rests at the bottom of the shaft, when in water - at the top. Placing contacts either at the bottom or the top such that the float would close them would allow you to electronically determine if the object is submerged or not.

The problem with Bluetooth is that the antenna would detune when your object is wet but not submerged making the problem more complex.

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