Police were called to an apartment building in the 4600 block of Haverford Place.
Two apartment buildings were evacuated as a precaution while police removed the device and detonated it.
Police say the device resembled a pipe bomb.
Residents were allowed to return after an hour.
Anyone with information about this incident is asked to contact the Delaware State Fire Marshal's at 302-323-5375 or CRIMESTOPPERS at 1-800-TIP-3333.