It really is as simple as that iff you never use your personal device for any business purpose.
[update] This was unclear: I'm saying this relationship is simple if and only if you have not used your devices for business purposes. If you have, you need only hope that none of the clauses in your agreements (you did have a lawyer review these?) cover it.
Even if I used it for work purposes occasionally, they can go to court and prove that in the process of getting a subpoena and I'll happily comply.
Due process exists for a reason; if you let any company examine your personal devices/data outside of a court order, they can use it for any purpose they want. Subpoenas are limited in scope, and everything is documented.
[update] This was unclear: I'm saying this relationship is simple if and only if you have not used your devices for business purposes. If you have, you need only hope that none of the clauses in your agreements (you did have a lawyer review these?) cover it.