Background of the Invention Fire doors are generally intended to have a lock assembly which provides access to an escape route (such as a fire escape) while inhibiting entry in the reverse direction.

Frequently unauthorised entry is achieved by tampering with the lock and/or striker member to retain the lock tongue in the retracted position.

Sensors which are provided with doors frequently detect whether the door is open or closed. Such sensors cannot determine whether the door has been tampered with to retain the lock tongue in the retracted position. It is also known to have sensors associated with the striker member or lock which determine when the tongue is extended, such as engaged within the striker member. It is also possible to tamper with the sensor associated or striker member to give a false reading in respect of whether the tongue is engaged within the striker member.

The above two sensors if used together are not coordinated to detect any anomaly.

Object of the Invention It is the object of the present invention to overcome or substantially ameliorate the above disadvantage.

Summary of the Invention There is disclosed herein a sensor assembly for a door having a lock with a lock tongue to engage a striker member, said assembly including: a first sensor to determine whether the door is open or closed, and to produce a signal indicative thereof; a second sensor to determine when the tongue is engaged with the striker member, and to produce a signal indicative thereof; and electronic means to receive the signals from the first and second sensors and to generate a signal indicating an anomaly when the first sensor produces a signal indicating that the door is opened and the second sensor produces a signal indicating that the tongue is engaged with the striker member.

Preferably the second sensor includes:

a housing to be positioned adjacent the striker member ; a tongue engaged member mounted in the housing and moveable relative thereto between a first position at which the tongue engaged member would not be engaged by the tongue, and a second position spaced from the first position and located therein when the tongue engaged member is engaged by the tongue; and a switch activated by the tongue engaged member to generate a signal indicative of the position of the tongue engaged member.

Preferably the tongue engaged member is pivotally mounted in the housing for pivoting movement between the two positions thereof.

Preferably the electronic means is a PC.

Brief Description of the Drawings A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a schematic view of a door and associated sensor assembly; Figure 2 is a schematic side elevation of a sensor employed in the assembly of Figure 1, the sensor being in a first position ; and Figure 3 is a schematic side elevation of the sensor of Figure 2 in a further configuration.

Detailed Description of the Preferred Embodiments In the accompanying drawings there is schematically depicted a door 10 pivotally mounted in a door jam 11. The door jam 11 has fixed to it or is formed with a striker member 12 which is engaged by the tongue of a lock 13. When the tongue is engaged with the striker member 12 the door is retained in the closed position.

Preferably the door 10 is a fire door providing one direction access.

Associated with the door 10 is a sensor assembly 14 including a first sensor 15 which generates a signal indicative of the position of the door 10, that is whether the door 10 is opened or closed. Typically the sensor 15 will include a magnet 16 which operates a reed switch 17.

The assembly 14 further includes a second sensor 18 which is more fully depicted in Figures 2 and 3. The sensor 18 generates a signal indicative of whether the lock tongue is engaged within the striker member 12.

The signals from the first and second sensors 15 and 18 are delivered to a PC 19.

The PC 19 would be used by security staff to monitor the door 10. For example if the first sensor 15 indicated that the door was open, and the second sensor 18 indicated that

the tongue was engaged with the striker member 12, then the security staff would know that the second sensor 18 had been tampered with.

The second sensor 18 includes a housing 19 which pivotally supports a tongue engaged member 20. The member 20 is mounted on a shaft 21 and pivots about a generally vertical axis. The tongue would approach the member 20 in the direction of the arrow 22 and cause it to pivot from the position showing in Figure 2 to the position showing in Figure 3. Mounted in the housing 19 is a switch 22 having an arm 23 which is pivotally moved by the member 20. Movement of the arm 23 generates the signal which indicates whether the tongue is engaged within the striker member 12.