By ground sensor do you mean something that will be in the ground physically(like seismic detectors) ? Or deployed “on the ground” as in “in field” ?
Are you looking to utilize the android phone and it’s internal components only or is external hardware ok?
The Android phone component, is its only duty to relay information from a separate external device that is collecting this information?
Does the device need to withstand any particular environmental hazards?
How long of a operating time is wanted for this device ? As in battery life, is the option for recharging in field wanted?
Is the goal to produce a cheap monitoring / proximity node (device) that easily incorporates the connectivity of a android phone only to relay pertinent information?

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