% empty out final sound vector
snd = [];

% define low-quality sampling rate (telephone quality of 8000 samples per
% second)
r = 8000;

% define length of each tone
l = 0.01;

% in a loop going from frequency 1000Hz to frequency 2000Hz in increments
% of 100Hz, build tones with different periods
% the concatenation of these tones produces a sound with increasing tones
for f=1000:100:2000
    snd=[snd, sin(2 * pi * f / r * [0:r * l])];
end

% reverse of above: produce a final sound with decreasing tones
for f=2000:-100:1000
    snd=[snd, sin(2 * pi * f / r * [0:r * l])];
end

% concatenate a few times to produce siren effect
snd=[snd,snd,snd,snd,snd];

% play back sound
wavplay(snd, r);