Comments on: Viral Alarm Failures https://www.epanorama.net/blog/2026/03/18/viral-alarm-failures/ All about electronics and circuit design Thu, 02 Jul 2026 22:07:19 +0000 hourly 1 http://wordpress.org/?v=3.9.14 By: Tomi Engdahl https://www.epanorama.net/blog/2026/03/18/viral-alarm-failures/comment-page-1/#comment-1880628 Sat, 27 Jun 2026 09:13:23 +0000 https://www.epanorama.net/blog/?p=199406#comment-1880628 why is the resistor there?

Steve Martin a resistor is needed to supply current to transistor base when alarm wire is cut. That base current turns on transistor that activates the buzzer.
If I were building this circuit, with rule of thumb I would use different resistance value: The circuit would work with resistance values from 1000 ohms to 10000 ohms OK without too much current draw.

]]> By: Tomi Engdahl https://www.epanorama.net/blog/2026/03/18/viral-alarm-failures/comment-page-1/#comment-1880627 Sat, 27 Jun 2026 08:51:48 +0000 https://www.epanorama.net/blog/?p=199406#comment-1880627 Surprisingly, unlike most AI-generated schematics, the foundational electrical logic of this circuit is actually correct, but it suffers from a massive real-world engineering flaw regarding component selection.
While the logic is sound, you should not build this exact circuit with the component values shown due to two major engineering issues:
​1. Massive Standby Battery Drain (resistor runs hot battery runs out quickly)
​2. Excessive Transistor Base Current (transistor can be fried when alarm goes on)
A 2000 mAh 18650 battery will be completely dead in about 54 hours (just over 2 days) without the alarm ever going off.

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