  We consider a three dimensional spatial network, where $N$ nodes are randomly
distributed within a cube $L\times L\times L$. Each two nodes are connected if
their mutual distance does not excess a given cutoff $a$. We analyse
numerically the probability distribution of the critical density
$\rho_c=N(a_c/L)^3$, where one or more nodes become separated; $\rho_c$ is
found to increase with $N$ as $N^{0.105}$, where $N$ is between 20 and 300. The
results can be useful for a design of protocols to control sets of wearable
sensors.
