Our Constitution only applies to the United States and as of yet, at least to my knowledge, unless they have permission from us, probable cause or a warrant, the police cannot just search anything of ours! The places presently searching items, i.e. theme parks, government buildings, etc. all have notices and reasons for the searches, so if you don't like it....don't go there!
The searches of backpacks/knapsacks in London, I can understand....as these are the items used to carry the last 8 bombs.....4 on 7/7 that caused a great deal of damage and 4 on 7/21 that, thank god, were duds.
CNN has just anounced the arrest of one of the 4 suspects they were looking for after yesterdays attack, at or very near the same place where the suspect was shot this morning!