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I have recently opened up 3 dead, battery-operated RF transceivers lying around, both wearable and key-chains. I've noticed that all three had components that looked like fuses (cartridge case), soldered down, that are quite large compared to the size of the circuit. See the pictures below. I'm not posting full circuit pictures because I don't know if I should, I can update if they are necessary.

Device 1:

Device 1

Device 2:

Device 2

Device 3:

enter image description here

I can't see why such a device will require a fuse, and I couldn't find any other common components manufactured in cartridge cases, maybe I'm not using the correct name. I don't see them on any applications notes or reference designs for the ICs used either.

I've tried to figure out how they are connected to the circuit, I don't have schematics and PCBs are more than 2 layers so they may not be complete, but see the schematics I've figured below.

Device 1:

enter image description here

Device 2:

enter image description here

Device 3:

enter image description here

Also, when I do a continuity test between the terminals of the components with a multimeter, resistance starts in ~50 Ohms range and goes down to short as I keep the probes on its terminals so my best guess is something for ESD protection, maybe Varistors or Thermistors?

Does anyone know what these components are and why they are there?

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  • \$\begingroup\$ Have you tried measuring the voltage across the components terminals to see if it is a battery? \$\endgroup\$ – Andy aka Jun 11 '18 at 8:56
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It's a tilt & vibration sensor SQ-SEN-200-IC (product page, manual).

enter image description here

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    \$\begingroup\$ +1 Nice find mister. \$\endgroup\$ – Andy aka Jun 11 '18 at 9:21
  • \$\begingroup\$ This is it, thank you. It seems like I couldn't find it when searching because it's not carried by most distributors. \$\endgroup\$ – shunt Jun 11 '18 at 12:33

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