A system and method for a patch-like, self-contained substance infusion device (700) which provides one or more substantially hidden patient needles (760) which can be placed in fluid communication with a fluid reservoir assembly (710) that includes a rigid bladder portion (712) used in conjunction with a non-distensible bladder film (740), such as a metallized film. The device (700) can be attached to a skin surface via an adhesive contact surface and a push button (780) activation assembly can then be used to remove an interlock (730), allowing a disk, or Belleville spring (735) assembly to apply an essentially even and constant pressure to the contents of a fluid reservoir assembly (710). The push button (780) activation assembly further allows the release of one or more spring-loaded patient needles (760) into the skin surface, and establishes a fluid communication path between the patient needles (760) and the pressurized fluid reservoir contents thereby delivering an infusion into the skin. The push button (780) activation assembly further allows the release of one or more improved safety mechanisms (794) after use which are driven by spring (793) and released by trap-door (790).