

More to the point. Making a cheap phone is not an affordable endeavour.
Linux phone makers such as pine have discovered this in the past. As your first products are going to be low demand. Running a business on the profit margins of lower priced phones becomes hard. It seriously limits your ability to gain investments. Making competition with similar priced products insanely complex.
In James bond movies yes. But most are written well before drones and very cheap thermal cameras.
It is pretty easy with modern equipment to monitor body heat in water. With the addition of AI very easy to ID human Vs fish both by shape and differing body temps.
But I’m no more a real general then yourself. So back to the armchair.