Electronics thefts on BART jumped 52% last year despite a 40% increase in arrests compared to 2016, the transit agency reported.
There were 417 thefts of phones or other mobile devices last year, far above the 274 in 2016.
BART police said some thefts involved force or fear, so they're also considered violent crimes. Those increased by 24%, from 279 in 2016 to 347 in 2017.
The agency said it is combating the crimes by using multiple high-quality surveillance cameras on trains.
"The word is getting out that BART is not a soft target for these thieves," BART Police Chief Carlos Rojas said in a statement. "If you take someone's phone, we have the tools to find you."
BART attributed a surge in arrests to the increased policing of crimes like fare evasion.
The agency cited or warned 8,223 people who did not pay for tickets in 2017, 88% above the 4,382 in 2016.
Auto thefts have decreased, however, and BART police reported a 13% drop in stolen cars throughout approximately 47,000 BART parking spots. Bike thefts have also gone down by 18%.
Rojas said the agency is in the process of hiring more police officers. The department hired 16 people in 2017.