The incident took place around 9:55 p.m. Sunday at the Home Properties of Bryn Mawr apartments in the 100 block of Charles Drive in Bryn Mawr, Pa.
Police say the woman was getting out of the shower and saw a man's hand holding a video recording device through the window.
The woman got back into the shower, covered up, and got out of the shower again. By that time, investigators say, the man was gone.
The woman then ran from the bathroom and called 911.
The only description is the hand was that of a white male. The victim could not identify the type of recording device.
"She believes it's a white male by the description of the hand and some type of recording device, she couldn't be sure exactly what it was because it was outside the screen, the window was cracked for ventilation while she was taking a shower," Radnor Police Sergeant Andrew Block said.
Officers searched the area but couldn't find a suspect. They believe the peeper stood on top of an air conditioner unit outside the apartment building..
"We always put out to be extra cautious to make sure the windows are locked, and make sure the drapes and blinds are drawn," Block said.
Police are investigating the possibility that this was a prank, but add they are still taking this crime "very seriously."
Anyone who has information, or has seen anything suspicious in the area, is asked to contact Radnor Township Police at 610-688-0503.