TULSA, Oklahoma - In Austin, Texas, a neighborhood lockdown is lifted after the 4th bomb explodes in the city this month.

The latest incident used a tripwire to activate the explosive.

“We are clearly dealing with what we expect to be a serial bomber at this point,” said Austin Police Chief Brian Manley.

Here in Tulsa, TPD’s bomb squad says if you see something, say something.

That is the same message Austin Police are sending out after Sunday night’s bomb left 2 young men injured.

Police say the bomber’s methods are becoming more sophisticated.

The fourth bomb was anchored to a metal sign near a hiking trail and equipped with a thin tripwire.

The first three bombs were in a different part of the city and the bombs were left on doorsteps.

Austin Police say they do not yet have a motive for the bombings.

Tulsa Police say to look out for suspicious packages.  Some signs to watch for include nontraditional taping, incorrect shipping labels, wires sticking out, or handwritten messages.

TPD says to call 911 if you find a suspicious package.