Patent ID: 7884313

Claim:
An intrusion detector including a sensor arrangement for detecting a liquid (C) applied on an exposed surface ( 100 , 120 , 160 , 170 ) to render the intrusion detector inoperable, the sensor arrangement comprising: at least one transparent elevation ( 12 , 22 , 32 , 42 , 52 , 62 , 72 ) formed on the exposed surface ( 100 , 120 , 160 , 170 ), wherein the transparent elevation ( 12 , 22 , 32 , 42 , 52 , 62 , 72 ) is made of a first transparent material (B), wherein at least one first facet ( 110 , 111 , 171 , 172 , 181 ) of the transparent elevation ( 12 , 22 , 32 , 42 , 52 , 62 , 72 ) defines a first angle (α, β) with the exposed surface ( 100 , 120 , 160 , 170 ), and wherein the first angle (α, β) is larger than an angle at which a total reflection occurs at an interface of the first transparent material (B) and air (A) and is smaller than an angle at which a total reflection occurs at an interface of the first transparent material (B) and the liquid (C) applied on the exposed surface to render the intrusion detector inoperable; at least one second elevation ( 12 , 22 , 32 , 42 , 52 , 62 , 72 ; 79 ) having a second facet ( 179 ) formed adjacent to the first facet ( 110 , 111 , 171 , 172 , 181 ) of the transparent elevation ( 12 , 22 , 32 , 42 , 52 , 62 , 72 ), wherein the second facet ( 179 ) defines a second angle with the exposed surface ( 100 , 120 , 160 , 170 ), which second angle is larger than 75° in order to enhance capillarity effects of the liquid (C) applied on the exposed surface to render the intrusion detector inoperable; a light source ( 13 , 23 , 33 , 43 , 53 , 63 , 73 ) arranged for emitting an incident ray (r) into a first direction such that the incident ray (r) passes through the exposed surface ( 100 , 120 , 160 , 170 ) into one of the transparent elevation ( 12 , 22 , 32 , 42 , 52 , 62 , 72 ) and the second elevation ( 12 , 22 , 32 , 42 , 52 , 62 , 72 ; 79 ), such that in a presence of the liquid (C) at one of the first facet ( 110 , 111 , 171 , 172 ) and the second facet ( 179 ), the incident ray is transmitted through the first facet ( 110 , 111 , 171 , 172 ) or the second facet ( 179 ), wherein in an absence of the liquid (C), the incident ray is reflected due to a total reflection at the first facet ( 110 , 111 , 171 , 172 ) or the second facet ( 179 ); and a light detector ( 14 , 24 , 34 , 44 , 54 , 64 , 74 ) for detecting the reflected incident ray (r′) at one of the first facet and the second facet to recognize that the liquid (C) is applied to the exposed surface to render the intrusion detector inoperable.