baldPrussian makes some excellent points. What you need to do is negotiate with your parents to find a mutually beneficial solution, one that gives you additional privacy but gives your parents assurance that you're not doing anything that will affect your health or safety. They are still legally responsible for you and more importantly they love you and don't want you to come to harm.
The best book on negotiating is "Getting to Yes" by Fisher and Ury. I suggest you read at least the summary (click here) because mastery of negotiation techniques will demonstrate your maturity in a way that simple words cannot.
The four principles of "Getting to Yes" are:
- separating people from the problem,
- focusing on interests rather than positions,
- generating a variety of options before settling on an agreement,
- insisting that the agreement be based on objective criteria
"Getting to Yes" has techniques for dealing with obstacles:
- when the other party is more powerful
- when the other party won't use principled negotiation
- when the other party uses dirty tricks
The first of these obstacles is the main one you're dealing with. When the other party is more powerful
the weaker party should concentrate on assessing their best alternative to a negotiated agreement (BATNA). The authors note that "the reason you negotiate is to produce something better than the results you can obtain without negotiating."[p. 104] The weaker party should reject agreements that would leave them worse off than their BATNA. Without a clear idea of their BATNA a party is simply negotiating blindly. The BATNA is also key to making the most of existing assets. Power in a negotiation comes from the ability to walk away from negotiations. Thus the party with the best BATNA is the more powerful party in the negotiation. Generally, the weaker party can take unilateral steps to improve their alternatives to negotiation. They must identify potential opportunities and take steps to further develop those opportunities. The weaker party will have a better understanding of the negotiation context if they also try to estimate the other side's BATNA. Fisher and Ury conclude that "developing your BATNA thus not only enables you to determine what is a minimally acceptable agreement, it will probably raise that minimum."[p. 111]
For the agreement to be objectively verified, I suggest a technique that was used during the nuclear arms reduction agreements of the 1980s, "Trust but verify." If all else fails, you can suggest to your parents that in return for removing controls on your devices, they can inspect your machinedevices at any time. You will get minute-to-minute privacy in exchange for occasional inspections to verify compliance and you can negotiate the terms of those inspections.
Good luck!