Last winter, Debbie Phelps carried pepper spray whenever she left her Decker Towers apartment. The corridors inside the low-income high-rise had become a magnet for the drug trade and squatters, thrusting Burlington's most urgent ills upon 160 elderly and disabled tenants. To feel safer, Phelps, who is in her late sixties and uses a walker, headed into the hallways with escorts and weapons for self-defense. But on a recent rainy December evening, Phelps entered the community room on the ground floor feeling excited. The building, she said, felt different now. No longer did trespassers occupy the laundry rooms and stairwells each night. The hallways were quieter. Residents were gathering to eat and sing karaoke. "It feels safe," Phelps said. "I don't have the stun gun or the pepper spray or any of that." Conditions at the St. Paul Street building have improved markedly from a low point last winter, when the building was overrun by drug users and homeless people looking for a place to stay warm. The changes have followed many months of dogged activism by residents. Their organizing last February prompted a coordinated response from public officials and led to hundreds of thousands of dollars in new security spending by Burlington Housing Authority, which owns the building, and the City of Burlington. While the efforts to improve security brought relief to Decker Towers' vulnerable tenants, the underlying regional crises of homelessness and addiction have not relented. So the challenges that its residents have endured are cropping up elsewhere. In recent weeks, squatters have taken up residence in office buildings, basements and apartment homes throughout the city. But at Decker, last month's karaoke night marked a return to neighborliness that residents say they had lost in recent years. The event was held in the same room where, last February, tenants voted to create a resident council to advocate on their behalf and form a neighborhood watch that would patrol the building to roust squatters. The council purchased a microphone and strobe lights for this happier affair, and residents used the community kitchen to serve spaghetti and cake. Four "dining room rules" were published on a whiteboard, starting with "No conflicts — please keep the peace," and ending with "Have a nice day and enjoy your meal." Standing at the microphone, council president Cathy Foley announced the evening's run of show. "Someone step up to the mic and…