When Arleen Dinneen fills out an application for National Night Out each summer, as she's done for nearly three decades, she always requests that county police arrive at her Centennial neighborhood in "anything with a siren."

"We usually get the [mobile] command vehicle or a fire engine, and the kids just love it," said Dinneen, who is organizing a 1-mile Fun Run on Tuesday for the evening that's billed annually as "America's night out against crime."

She expects the Ellicott City event, one of 26 planned around the county Tuesday, to draw 200 neighbors of all ages in a show of solidarity.

While National Night Out is about Americans banding together to raise awareness of crime in their communities, the event isn't spurred by rising crime in Howard County, since crime is down, said county Police Chief William McMahon.

Instead, its impetus locally is more a question of math.

"We have about 300,000 residents and tens of thousands of people passing through here each day, and we have 445 sworn police officers," he said. "We can't keep the county safe on our own. Howard County is a very safe place to live, and that's not by accident."

Howard's police force has been cultivating neighborhood partnerships for 28 years during National Night Out, which was started in 1984 "to send a message to criminals letting them know that neighborhoods are organized and fighting back," according to the organization's website.

Last year, 37 million people participated in 15,000 communities across the United States, national organizers say.

The county's main Night Out celebration will be held Tuesday for the first time at the year-old North Laurel Community Center from 6 p.m. to 9 p.m. Max Impact, theU.S. Air Forcerock band, will perform, and the county police helicopter will land. A skateboard trick competition will also be held and clowns will make balloon animals, among other events.

Twenty-six registered block parties involving 2,000 people will be held the same night around the county at events that vary from swim parties to cookouts to ice cream socials.

But participation in Howard "is not necessarily generated by crime data and whether it's up or down," said Sherry Llewellyn, county police spokeswoman. "It's about building unity in your community."

The county ended last year with the lowest "raw number" of residential burglaries since 1999, McMahon pointed out.

In fact, Part 1 crime — which includes homicide, rape, robbery, aggravated assault, breaking and entering, larceny/theft and motor vehicle theft — has been declining since 2007, according to Police Department statistics, except for an uptick in 2008.

The total number of Part 1 crimes per 100,000 county residents rose from 2,784 in 2007 to 3,151 in 2008. Figures then declined annually from 2,715 in 2009 to 2,546 in 2010 to 2,454 last year. The total number of offenses dropped from 18,500 to 17,500 during that five-year period, according to police reports.

But what's troubling about residential burglaries, the chief said, is that nearly half occurred when residents left garage doors open or cars unlocked in driveways. People have even reported that their homes have been burglarized through an open garage door while they were in their backyards mowing grass, he said.

"These are crimes of opportunity, and they can be reduced even further by doing simple things like locking the door that leads from your garage to your house," McMahon said.

"We need residents who see someone walking along a street with a TV or golf clubs to call us. And we need neighbors to connect with one another more than ever with people working more than one job and using social media to interact.

"Even though burglaries are down, McMahon said, "there are still a lot of them taking place at residences and businesses."

Llewellyn said National Night Out provides officers the chance to engage with citizens in a setting that doesn't involve a crisis situation.

"There aren't any formal presentations, and residents shouldn't bring problems to discuss," she said.