As per the New York City Department of Parks and Recreation, metal detecting in New York City parks can be done but is restricted to open areas. You must apply for a permit with a copy of your photo ID showing your current address. If your permit is lost, you should file a police report, which will take the place of your old permit when you reapply for a permit the following year.
On top of obtaining a permit, you must also report any significant object finds to the Urban Park Service within 48 hours of discovery. Any identifiable property found by a metal detectorist must be turned over to the Parks department, who then in turn will deliver the items to the New York Police Department local precinct while the property owner is located.
If the owner cannot be located, the item will be returned to the finder. You must only use hand tools that can be operated by one hand when digging for targets. You must not dig within 25 feet or drip line of trees, and you may not dig in athletics fields, manicured lawn areas, freshly seeded lawns, monuments, tracks, golf courses, flower beds, gardens, woodlands, native vegetation areas, monuments, or any other area where signage indicates restriction.
Remember: do your research before Metal Detecting in New York. You do not want to be caught detecting in restricted areas!
Always make sure you know the laws and rules and have the proper permit. You can get into a whole lot of trouble otherwise. If you are caught metal detecting in restricted areas or without a permit, you can have your equipment and finds confiscated, and could even serve jail time. It simply is not worth it!