cost to install surveillance cameras in public places

kragen at kragen at
Thu Oct 13 00:37:01 PDT 2005

Suppose you wanted to plant a hidden camera for some long period of
time and capture photos of all that went past.  You'd like to never
again have to enter the place where it's hidden, and only visit it
rarely; you'd like it to be small; and you'd like it to last a long
time.  For example, the book "The Social Life of Small Urban Spaces"
was based on a few years of research in this vein using Super 8
cameras for time-lapse photography.  It appears to me that this
equipment should now be incredibly cheap.

USB "webcams" that capture 100-kB 640x480 JPEGs are on the order of
$10.  I think 4-port USB hubs (again, on the order of $10) contain all
the hardware necessary to act as USB host controllers; one could
imagine integrating the USB hub hardware with a small single-board
computer with SD/MMC and Bluetooth interfaces, for a total cost on the
order of $50 plus up to 4 cameras and their USB cables, and an MMC
card ($50-$110).

This device would presently be limited in smallness only by the size
of its power supply, USB ports, and multi-chip integration, so it
could be concealed in many places.  You could probably run it on 200mW
when running (for less than a second) and <1mW when idle.

You could drop by periodically with an inconspicuous Bluetooth device,
such as a cellphone or laptop, to download the pictures (say, 4
cameras * 100kB/shot/camera * 4 shots / minute * 60 minutes/hour * 24
hours/day = 2.3GB/day; but one shot per minute is only 144MB/day).
Anyone snooping over Bluetooth at the time could tell that a lot of
data was being sent over Bluetooth (1megabit/sec? not sure; but at
that speed you'd have to spend 2300 seconds in the vicinity.)

Alternatively, you could use a directional antenna from hundreds of
meters away (the "Bluesniper" folks managed to do 1km.)

An adaptive surveillance algorithm could shoot four times per minute
until the data card was full, followed by twice a minute (replacing
every other old shot, starting with the oldest) until the data card
was all full at twice a minute, then once per minute (thinning out old
shots to once a minute) until it was full again, etc.

Supposing that USB 12Mbps transfers were the limiting factor, you'd
need about 67ms of "on time" per shot, or (according to my 200mW
estimate above) 13.4 mJ.  My laptop's Li-ion battery supposedly holds
around 46Wh, or 165kJ (abridged info below):

$ cat /proc/acpi/battery/BAT1/state
present rate:            1227 mA
remaining capacity:      2579 mAh
present voltage:         11300 mV
$ cat /proc/acpi/battery/BAT1/info
design capacity:         4500 mAh
last full capacity:      4067 mAh
design voltage:          10800 mV
model number:            XM2018P02
battery type:            Li-ION

11.3V * 4.067Ah = 46Wh.

On that basis, my laptop's battery could power 12 000 000 invasions of
privacy by this system --- saving that many camera shots to an MMC
card.  It might only be able to power 4 000 000 invasions of privacy
if it had to transmit them all over Bluetooth.  Still, that's nearly
six months in the four-shots-with-four-cameras-per-minute maxi
configuration described above, where you'd have to come download up
your photos at least once a day, and at one camera shooting once per
minute, it would last 8 years.

(I'm assuming that the webcams power up instantly.  This may be

Obviously you could do a similar job with audio surveillance, but
ironically, this may consume more storage and power; minimally
comprehensible speech is 10kbps under the best of conditions, so you'd
need at least 108MB/day, and probably several times that to get
anything useful.  You'd need some very-low-power constantly-on device
to buffer the audio so you wouldn't have to run the CPU all the time.

A similar system, but without the cameras or other transducers, could
serve as a maildrop or backup server (for data with high value per
byte, obviously).

We can anticipate that the power and monetary cost of data storage and
transmission will decrease considerably more before Moore's Law runs

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Eugen* Leitl <a href="">leitl</a>
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