Yes and antenna can "wake" up a scanner, it can also not be what you need.
You buy an antenna based on the frequencies you want to monitor.
Remtronix makes some good ones as do many other companies. tell us what frequencies you want to monitor, how far away you are from the systems and if there are any mountains or tall building in between you and the transmitters. Use the the database in RR to research.
Also with any antenna on the scanner reception in a car can be poor as can inside a home with metal roof, siding etc. you need the right antenna for the situation.