(NewsNation) — Drones have been spotted for more than a month in multiple states. Although the number of sightings around the United States has dropped recently, and the FBI has dismissed many of the 5,000 reported as manned aircraft, the agency told reporters there are still more than 100 sightings that need to be investigated. Concern grew after a large number of drones began flying over sensitive military sites in New Jersey in mid-November. White House and Pentagon officials have maintained they don't pose a threat, but lawmakers and residents still have questions. Watch: President Joe Biden’s full remarks to a joint session of Congress Why is it hard to identify drones?  Drones can be hard to track using traditional radar systems, according to the Center for Strategic and International Studies, as they are best at monitoring objects with large radar cross sections and higher altitudes. While these radar systems can detect drones, they can mistake these objects for birds because they cannot classify detected objects on their own, the Center for Strategic and International Studies writes. In addition, drones might fly erratically or quickly change speeds. While drones that weigh more than 250 grams are required to broadcast identifying information, certain ones, like those operated by the United States government, are not required to do so.  Maj. Gen. Patrick S. Ryder, the press secretary for the Department of Defense, told reporters at a December press briefing that military bases overseas can use surveillance methods to address a drone's origins. However, this power is limited in U.S. airspace because of domestic surveillance laws. Most drones are operated through radio frequency transmissions or satellite-guided GPS navigation, and that can be a source of information about who is operating them, Ryder said. If they aren't controlled this way, that can give officials another clue, he added. White House National Security Communications Adviser John Kirby said earlier this month that after examining the data and looking at tips from concerned citizens, what people saw was a combination of lawful commercial drones, hobbyist drones, law enforcement drones, manned fixed-wing aircraft, helicopters and stars. "We have not identified anything anomalous or any national security or public safety risk over the civilian airspace in New Jersey or other states in the Northeast," Kirby said. Officials are continuing to work on investigating, Kirby said, and "continue to support state and local authorities with technology and law enforcement support." What has been done in states with drone sightings?  Flight restrictions were requested by federal security agencies and issued by the FAA over 22 areas of New Jersey. These restrictions, which the U.S. Department of Homeland Security said are being done "out of an abundance of caution," are in effect until Jan. 17, 2025. New Jersey deployed drone-detecting devices following the sightings. New Jersey Gov. Phil Murphy said they found "little to no evidence" of anything nefarious or threatening. New York and Pennsylvania officials also requested drone-detecting equipment from federal officials. Senate Majority Leader Chuck Schumer, D-N.Y., tried to speed a bipartisan bill to allow local law enforcement agencies to track aerial drones, but this move was blocked after Sen. Rand Paul, a Kentucky Republican, objected to its passage. Ex-NASA astronaut encounters mysterious flying orbs 9,000 ft. in air What federal regulations are there for drones?  The Federal Aviation Administration requires any recreational drone weighing more than about a half-pound, as well as all drones flown under Part 107, to be registered with their agency. A registration number has to be displayed on the outside of the drone. It is generally legal to fly a drone in most locations, but recreational flyers need to take a basic safety knowledge test. Rules for recreational flyers include flying below 400 feet, having operators keep the drone in sight, avoiding other aircraft and not causing safety hazards to people or property. Those flying a drone for purposes such as getting a video need to have a drone pilot certificate. Flying within controlled airspace around airports, designated national security sensitive facilities, certain military bases, infrastructure and national landmarks and places covered by Temporary Flight Restrictions is prohibited. It is also illegal to shoot at drones. Experts say it would be a risk to public safety because of debris potentially falling on people as well as the possibility that the objects are legitimate aircraft. What have officials said about drones?  Federal officials, including Homeland Security Secretary Alejandro Mayorkas, have repeatedly said there are no signs that any drone operators have shown bad intent. Defense officials have seen no indication that the drones are being controlled by a foreign country. The FBI said they don't believe the drones are U.S. military property, either. Lawmakers from both parties have called for more transparency over drones, with some introducing legislation on it and urging public briefings. “I think they need to be a lot more candid about what’s going on," Rep. Steve Scalise, R-La., said. NewsNation partner The Hill and The Associated Press contributed to this report.