Algorithm 1 Human Activity Classification Algorithm.

while true do

Acquire accelerometer readings, Ax Ay Az are three components along three axes;

Calculate acceleration $A=\sqrt{A_x^2+A_y^2+A_z^2};$;

Calculate σ, covariance of A in a 3 s sliding window;

if A ≥ δ1 and σ ≥ δ2 then

{δ1 and δ2 are two thresholds.}

return Walking;

else

if |Az| ≤ ε then

{ε is a small number closed to zero.}

return Lying;

else

return Standing;

end if

end if

end while