Door alarm circuit Diagram

This is a door alarm circuit.I have used a magnetic-reed switch for this.When the door opens the buzzer will give a beep beep sound.Changing R2 and C2 The period of generating beep sound can be changed.According to the values of this circuit you can get that sound for 4 or 5 seconds.double the value the you can double the time.Note

# this circuit operate with 9V battry.

#Build this circuit on a PCB

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Cheap Bicycle Alarm Schematics Circuit

The author wanted a very cheap and simple alarm for some of his possessions, such as his electrically assisted bicycle. This alarm is based on a cheap window alarm, which has a time-switch added to it with a 1-minute time-out. The output  pulse of the 555 replaces the reed switch in the window alarm. The 555 is triggered by a sensor mounted near the front  wheel, in combination with a magnet that is mounted on the spokes. This sensor and the magnet were taken from a cheap bicycle computer. 

Circuit diagram :

Cheap Bicycle Alarm Circuit Diagram

The front wheel of the bicycle is kept unlocked, so that the reed  switch closes momentarily when the wheel turns. This  triggers the 555, which in turn activates the window alarm. The circuit around the 555 takes very little current and can  be powered by the batteries in the window alarm.  There  is just enough room  left inside the enclosure of the window  alarm to mount the time-switch inside it. 

The result is a very cheap, compact device, with only a single cable going to the reed switch on the front wheel. And the noise this thing produces is just unbelievable! After about one minute the noise stops and the alarm goes back into standby mode. The bicycle alarm should be mounted in an inconspicuous place, such as underneath the saddle, inside a (large) front light, in the battery compartment, etc.

Hopefully the alarm scares any potential thief away, or at least it makes other members of the public aware that something isnt quite right. 

Caution. The installation and use of this circuit may be subject to legal restrictions in your country, state or area.

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Simple Gate Alarm

Description:
A cheap and easy gate alarm comprised of a single CMOS Integrated Circuit.

Figure 1 characterizes a low cost and simple Gate Alarm, that is supposed to run off a small universal AC-DC energy supply.

IC1a is a fast oscillator, and IC1b a gradual oscillator, which can be blended through IC1c to emit a high pip-pip-pip warning sound when a gate (or window, and so on.) is opened. The circuit is meant no longer so much to sound like a siren or warning tool, but quite to present the impression: \"You were now noticed.\" R1 and D1 may be ignored, and the value of R2 perhaps decreased, to make the Gate Alarm sound more like a warning software. VR1 adjusts the frequency of the sound emitted.

IC1d is a timer which lead tos the Gate Alarm to emit some 20 to 30 further pips after the gate has been closed again, sooner than it falls silent, as if to say: \"Im more clever than a easy on-off tool.\" Piezo disk S1 may be changed with a LED if preferred, the LED being wired in collection with a 1K resistor.

Figure 2 shows how an bizarre reed swap may be transformed to close (a \"normally closed\" swap) when the gate is opened. A continuity tester makes the work straightforward. Note that many reed changees are refined, and subsequently wires that are soldered to the reed change should not be flexed at all near the swap. Other forms of swapes, one of theses microswitches, can be used.

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