The right to privacy is a complicated piece of law. Most people assume that privacy is an inalienable right, like free speech or freedom of religion, but it is not. The right to privacy is much more circumspect, and it is severely curtailed when it concerns your employer. Generally, your employer is entitled to search any area that he or she owns.
Typically, this breaks down into two general categories: places that are owned by you and places that are not. For example, your employer has a right to search any office, desk, cabinet or locker that you use if it is owned by the employer. It is irrelevant if you store personal belongings on business property because your employer has a right to know what is going on their property.
This also includes your computer and email accounts. If you use a company car, then your employer is free to search it. Similarly, if you store personal photographs or send personal emails from your work computer, then your employer is also permitted to search your hard drive.
Monitoring communications is a bit trickier because some states require mutual consent. This means that in order for your employer to record and review your conversations, your employer must have your express consent. Of course, this does not forbid your employer from firing you if you refuse. This is also true of drug tests. Although they may seem invasive, they are nevertheless permitted.
However, your employer generally must have good cause to submit you to a polygraph test. Good cause is usually limited to economic crimes against your employer, like fraud or embezzlement. There is, however, an exception if you work in either the security or pharmaceutical industry.
If you believe that your employer violated your right to privacy then you may want to consult with an employment attorney. Your employer does have a right to search their own property, but that right typically stops there. You may have an actionable claim for wrongful termination or harassment if your right to privacy was infringed. Privacy is a balance between your needs and your employers, which does not mean that your employer may search anything they like.