An unofficial memo is circulating through NYPD precincts warning officers to be on guard against perpetrators who conceal blades in their cell phones and other hand-held devices. The handout shows how you can easily hide a razor blade in the battery compartment of a T-Mobile Sidekick, and also reminds officers about the recent arrest of a suspect in Harlem who converted his cell phone into a stun gun. A police source tells amNY that the improvised weapon "was unlikely to cause much harm, as the jolt was described as low-level." And then there are the hospital meal trays you've got to watch out for! Cops assigned to guard hospitalized prisoners are being warned that meal trays have a vanity mirror that can easily be fashioned into a makeshift shiv. The vanity mirror is in a second-level compartment and that "can pop up for easy use by a patient." Of course, one way to eliminate that threat would be to serve the prisoners' meals on regular trays, but then officers would be forced to guard prisoners with food stuck between their teeth, and we don't pay them enough for that.