A strain indicator of the type wherein a change in length of a strain member produces a change in color of a visual indicator. An indicator area and a light-absorbing indicator fluid are encapsulated in a member that also includes a window. The capsule is fastened to the strain member with an adhesive. A change in length of the strain member causes the indicator area to become separated from the window with the result that light-absorbing indicator fluid is caused to flow between the indicator area and the window.

A connecting member comprises a rod-shaped body having a head and/or thread on the outer periphery for integrally connecting a plurality of members and a containing hole opened at one end thereof and extended longitudinally, a rod disposed in the hole so as to fix at its inner end to the inner end of the hole, a transmissive window fixed to the opening of the hole, and a fluid holding member holding a colored fluid and pressed by the open side end of the rod on the window. When a longitudinal strain developed in the body the rod release the holding member from under pressure so that colored fluid covers the open side end of the rod.

A strain indicator of the type wherein a change in length of the strain indicator gives a visual indication of the change in length. The strain indicator has an elongate strip supported at either end such that the curvature of the strip changes with changes in strain. An optical indicator such as a reflector is mounted on the strip so that the change in curvature can be measured.

A device for indicating when a lug nut has come loose on an automobile wheel. In one embodiment, the device operates by detecting relative movement between the lug nut and the axle stud on which it is mounted. In a second embodiment, the detected relative movement is between the lug nut and the wheel itself. In the preferred embodiment, the device has a first member with an open-ended channel and second and third members slideably received in it. The second member operates in cooperation with the sides of the channel and one of the springs to hold the third member in a retracted or cocked position when the lug nut is in its preferred, tight position against the wheel. Thereafter, should the lug nut come loose and move relative to the stud, the second member will follow or move under the force of its spring outwardly to maintain contact with the free end of the stud. In doing so, the third or indicator member is released to move in the opposite direction under the force of its spring to protrude beyond the outer surface of the lug nut where it can be easily and quickly seen or felt by hand. In the second embodiment, the second or follower member abuts the wheel itself rather than the free end of the stud but otherwise operates in the same manner.

A security device for preventing or indicating the tampering with a joint in a supply pipe, e.g. to a gas meter, comprises two or more members which fit together around the joint. The members have mutually interdigitating parts through which a blind bore is provided and which houses a glass phial containing a dye. Displacement of the members from the assembled configuration breaks the phial, thereby releasing the dye which stains the members so that the tampering is readily detectable.