"It echoed quite a bit through the hills that we have here," resident Dave Koehn told KTVU. He was among those who called 911 at about 5 p.m.
"There's got to be more here than meets the eye," Koehn acknowledged. "There's a lot of uncertainty about what is going on."
Deputies arrived and detained 43-year-old Laureen Mason in a patrol car, as a warrant was sought for the property at 174 Pacheco Avenue. Crime tape went up across the driveway and several patrol cars stood sentry.
Mason is the same woman accused three weeks ago of possessing and setting off explosives at the same property. She apparently made bail of $50,000 on Feb 13, the same day she was arrested.
Whether she has acquired new explosives, or some were overlooked in the first search is unknown.
"If she's come back into possession of explosive devices, we need to know what's happened in the past three weeks," Sheriff's Lt. Doug Pittman told KTVU, "but I assure you when we did the search last time, we did a very thorough search of the house and property."
In the last search, with assistance from the U.C. Berkeley bomb squad, almost 90 explosive devices and chemicals used to make explosives were found and removed by technicians.
"Well, I didn't think it was going to be an issue again," neighbor Emily Koehn told KTVU. "Last time, it was pretty crazy."
The bomb squad was brought to the woodsy neighborhood the first time after a traffic stop of Mason and her boyfriend nearby. A search of the car turned up a backpack containing four explosives.
By that time, she was already under suspicion because of explosions neighbors had heard, and because she had allegedly used explosives to threaten or intimidate.
"I don't know what kind of person has explosives in their house," Emily Koehn added. "But this is a really nice neighborhood and it shouldn't be an issue here."
Neighbors said the house is owned by the suspect's mother, who has moved out of state.
Given what has been found previously and what the new search might reveal, neighbors aren't sure how alarmed they should be.
"I don't know if these are devices that could just take off a couple of fingers. Or they could actually be fatal. I don't know," mused Dave Koehn.
"Last time, the devices found were equal to a half stick of dynamite," clarified Lt. Pittman. "So are they a threat? Absolutely."
Mason also faced a child endangerment charge because her five-year-old daughter lives with her. Authorities said the child was not at the home when they responded Monday evening.