tilt sensor alarm

Tilt Sensor Alarm Circuit

Ultra simple circuit of the tilt sensor alarm presented here can be fabricated using readily available inexpensive components. The circuit is a true transistor based design. Home made Tilt sensor for this circuit is an ordinary little glass/plastic bottle with two metal needles inserted through its cap, and a small quantity of water inside.
You can also try your own ideas to make the tilt sensor. A 9V alkaline battery is enough for powering the whole circuit.

Tilt Sensor Circuit Schematic

tilt sensor alarm schematic

Usually, transistor T1 is in inactive state. When the sensor assembly is tilted, both needles inside the sensor (bottle) are short circuited by the water and a positive voltage is available at the base of T1 and it becomes active. Activation of T1 causes the activation of next transistors T2 and T3. After this, T2 supplies constant bias for T1 to make it latched and T3 triggers the SCR(T4) which inturn energises the active piezo-sounder(BZ1). Once activated the circuit can be deactivated by depressing the power/reset switch S1.

Preset pot P1 is deliberately added here to adjust the circuit sensitivity. This may become necessary if you are trying a different (readymade) tilt sensor. Similarly,SCR(T4) and piezosounder (BZ1) may be replaced with near equivalent parts. Resistor R3 (100-150 Ohm) is optional.


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  • T.K.Hareendran

    @Colin Mitchell:

    Please keep your language clean. I am not a circuit designer receiving remuneration from you. Reserve your cheap replies for those working with you,if any.


    The one and only magazine publishing Colin’s 70’s- model circuits is Electronics Maker (published from India, not from Australia). Since the magazine pays nothing for contributors,they can play with the poor stuff. His bundled-submission has been rejected by EFY magazine only because of its “standard” (I’ve solid evidence in this matter,and ready to publish if requested). I know the reason why all Indian, Australian & UK magazines closed their doors and throw off this old demon!

    @ Site Owner:

    I request the site owner to cast off guys like Colin Mitchel from posting irrelevant (and biased) comments here. I consider this precious space as a platform for talking & learning about electronics. Do not promote others cheap business trickery!

  • Colin Mitchell

    That’s only the first problem. Of course you should have protection if the probes touch.
    T1 and T2 have no current-limiting resistor.

  • Colin Mitchell

    Touch the two terminals together and let me know what happens

    • T.K.Hareendran

      Who can touch the needles inside a sealed bottle? Your intention is just to publish irrelevant (and dirty) comments here (in your name, and using other “fake” names) to attract visitors to your website!

  • Diya

    Tested the circuit exactly as shown in the article with water filled in my homemade tilt sensor (small bottle with needles). Working well, and no fumes.

    Electronics is more of an Art than a Science. Use trial and error and explore what will happen if …..

  • Colin Mitchell

    Nishima – you don’t know what you are talking about.

    The circuit DOES NOT WORK. The first transistor will blow up as soon as the tilt sensor is moved.

  • Nishima

    Any one can come up with ideas. But the implementation is very difficult, that is why many self-proclaimed electronics gurus just posted cheap comments and disappeared. Why they failed to publish their own improved circuits here? “typing culture less comments is easier than building a working circuit”. All of them including Colin knows this well!

    Here the base resistor is not very important because the sensor is a sealed one.

  • Colin Mitchell

    T.K. Hareendran has no idea how to produce electronic circuits. Do not build this circuit.

  • Mihai

    As a matter of fact there are some parts completely useless in this schematic.

    This circuit(Tilt Sensor Alarm) could be made fully functional using only the thyristor, a gate current limiting resistor and the 100nF capacitor. All the rest are useless and moreover T1 and T2 will blow up(at least will drain the battery for sure!!!) because there is no base-emitter-collector limiting resistor.

    Also, the 100Ω resistor will drain the battery in no time. This resistor should be at least 1.2kΩ in order to mantain the holding current(max 6mA).

    This schematic is hilarious. The author wasn’t aware of what he was doing.

  • Clive Grant

    Yes, a resistor is required in T1 base supply to drop the power supply voltage. Otherwise, catastrophic failure of T1. It looks as if the circuit diagram has been drawn by a 7 year old novice.

  • Mihai

    A limiting resistor(4.7kΩ minimum) must be tied in series with the tilt sensor, otherwise +9V is applied in the base of T1. Needless to say that T1 will blow up in case of using a mercury or a ball switch tilt sensor, for example.

    Likewise, a limiting resistor(>1kΩ) in the emiter of T2 won’t hurt.

    Anyway, you can get the same results with only one transistor and the SCR(BT169). This schematic is useless complicated.