A private investigator is conducting surveillance on a subject from a public street. The subject enters their private backyard, which is visible from the street over a low fence. Can the PI continue to observe and record the subject's activities in the backyard?

1. No, because the backyard is private property
2. No, this constitutes trespassing
3. Yes, but only if the investigator obtains a warrant
4. Yes, if the activities are openly visible from a public vantage point without any special aids, as there is no reasonable expectation of privacy.