CHICAGO (CBS) — Police are warning bank customers to be careful, after a string of robberies at ATMs on the South Side.

WBBM Newsradio’s Nancy Harty reports one robber used a knife, another implied he had a gun; most were alone, and all took place at ATMs in the lobbies of different bank branches.

Police have issued a community alert warning of the robberies at 84th and Stony, 86th and Cottage Grove, 69th and Ashland; at 87th and Halsted, and at 87th and Champlain.

CBS 2’s Suzanne Le Mignot obtained surveillance video of one of the robberies. A woman walks into a Chase branch near 87th and Cottage to use the lobby ATM. Seconds later, a man follows her in.

Then, the man runs out, jumps into a car and reverses all the way out of the parking lot, onto the street. Seconds later, mall security arrives.

In each case, there have been between one and three offenders.

“This is so dangerous, because I come up here all the time and you never know who’s behind you,” ATM user Beverly Jenkins says.

The police alert cautioned bank customers not to use ATMs alone, and to try to use ATM lobbies that have locking doors.

If confronted by a robber, the victim should comply with all demands, and try to remember any unique identifying characteristics.