<P> A pressure cooker bomb is an improvised explosive device (IED) created by inserting explosive material into a pressure cooker and attaching a blasting cap into the cover of the cooker . </P> <P> Pressure cooker bombs have been used in a number of attacks in the 21st century . Among them have been the 2006 Mumbai train bombings, 2010 Stockholm bombings (failed to explode), the 2010 Times Square car bombing attempt (failed to explode), the 2013 Boston Marathon bombing, and the 2017 Manchester Arena bombing . </P> <P> Pressure cooker bombs are relatively easy to construct . With the exception of the explosive charge itself, most of the materials required can be easily obtained . The bomb can be triggered using a simple electronic device such as a digital watch, garage door opener, cell phone, pager, kitchen timer, or alarm clock . The power of the explosion depends on the size of the pressure cooker and the amount and type of explosives used . </P>

What kind of bombs were used in boston